There are a few things I always think should be considered when using a
workflow.

Patterns

Always, always add a timer after the Begin activity.
Avoid Switches because they don't update when their conditioned
field changes.
Avoid Email Activities, instead, opt for Event activities.

Here I have a diagram showing a timer added after the Begin activity.
This timer returns the user's session so it seems immediately which is
great for user experience. But, it makes your workflow dependent on
the events queue. If that goes down, this is the least of your worries.

Next, I have a Diagram showing the Switch, if some changed the
variable/field values of "Standard" to "Mechanical" the workflow
activity won't know to use the new value until you check it out, then
recreate the switch, and check it back in. Because of this, I use If
activities. It is more activities but, because the If activities are
scripted, they won't break when you change the variable. If activities
used to allow you to create any number of "result" boxes below, one of
them being an "else" but now If's only allow yes and no for results.
Below is an example Switch Workflow and it in the If pattern.

Last but not least, because you should avoid checking out
workflows, always use events in workflows if you need a workflow to
generate a notification. There are some extra steps to take to do
this but it's well worth it because now you can use the notification
records how they are for the rest of the system, you can generate the
notification without the workflow by running the following in a business
rule or any server-side script;

gs.eventQueue('custom.notification', current, 'parm1', 'parm2');

Now if you were using variables and are not sure how to pass more than
two parameters, don't fear. Make your first parm a JSON.stringify
object. Sure you'll need to JSON.parse the object in the notification,
but now you can pass everything in a way not dependent on the workflow.

Activities

Type	Activity	Description
Subflows	Parallel Flow Launcher	Launches multiple subflows in parallel.
Utilities	Branch	Splits the workflow into multiple transition paths from a single activity.
Utilities	Join	Unites multiple execution paths into one transition.
Utilities	Return Value	Returns a value to a parent workflow, when run from a subflow.
Utilities	Run Script	Runs the specified script in the scope of the workflow version.
Utilities	Set Values	Sets values on the current record when the workflow quiesces or ends.
Conditions	If	Checks a condition or script to determine if a Yes or No transition should be taken.
Approvals	Approval Action	Performs an approval action on the current task.
Approvals	Approval Coordinator	Creates an approval whose outcome depends on the outcome of one or more child activities.
Approvals	Approval - Group	Creates approval records for each member of a specified group.
Approvals	Approval - User	Creates one or more individual user approvals.
Approvals	Manual Approvals	Watches and manages any approvals that users add manually outside of the workflow process.
Tasks	Catalog Task	Creates a service catalog task record.
Tasks	Create Task	Generates a record on any of the tables that extend Task [task].
Timers	SLA Percentage Timer	Pauses the workflow for a duration equal to a percentage of an SLA.
Timers	Timer	Pauses the workflow for a specified period of time.
Notifications	Create Event	Adds an event to the event queue, but does not immediately fire the event.
Utilities	Lock	(no use-case) Prevents other instances of this workflow from continuing past this activity until the lock is released.
Utilities	Unlock	(no use-case) Releases a lock that was previously placed by the Lock activity.
Utilities	Log Message	(no use-case) Writes a message to the workflow log.
Utilities	Log Trace Message	(no use-case) Writes a trace message to the workflow log.
Utilities	REST Message legacy	(use run script instead) Enables an administrator to override the REST endpoint or supply the variables configured in the REST Message module.
Utilities	SOAP Message legacy	(use run script instead) Uses SOAP messages defined in the System Web Services plugin and can call the messages using a MID Server.
Utilities	Turnstile	(no use-case) Limits how many times a workflow can pass through the same point.
Tasks	Add Worknote	(use set values instead) Adds text to the Worknotes field of the current incident record.
Tasks	Attachment Note	(use run script instead) Adds an attachment to the current record.
Notifications	Notification	(no use-case) Sends an email or SMS message to specified users or groups.
Conditions	Switch	(no use-case) Checks if the value of a passed field or variable is equivalent to one of several case values.
Conditions	Wait for condition	(no use-case) Causes the workflow to wait at this activity until the current record matches the specified condition.
Conditions	Wait for WF Event	(no use-case) Causes the workflow to wait at this activity until the specified event is fired.
Approvals	Generate	(no use-case) Immediately creates task or approval records from any task or approval activities placed this.
Approvals	Rollback To	(no use-case) Transitions directly to the activity specified by the outgoing transition line arrow.
Orchestration	JDBC	Allows you to execute ANSI SQL statements or stored procedures on a target database.
Orchestration	SOAP web service	Create a custom SOAP activity.
Orchestration	Javascript Probe	Has the same functionality as making 'Packages' calls into standard Java libraries.
Orchestration	PowerShell	Return data to a workflow from a host using Microsoft PowerShell.
Orchestration	REST web service	Use this procedure to create a custom REST web service Orchestration activity.
Orchestration	SFTP	Executes basic SFTP commands on a remote server.
Orchestration	probe	Runs a probe on the target host that is configured to return specific information.
Orchestration	SSH	Extracts data from a target host that uses the SSH network protocol.
Orchestration	run script	Runs any script.
Orchestration	JMS	Create a custom JMS activity to retrieve or send messages to external systems using the Java Messaging Service.
Notify	Forward call	Forwards a Notify call to an E.164-compliant phone number.
Notify	Input	Creates a phone menu by presenting a list of options on a Notify call.
Notify	Hangup	Disconnects an active Notify phone call.
Notify	Play	Plays a sound file on a Notify call.
Notify	Record	Records audio from a user on a Notify call.
Notify	Reject	Rejects an incoming Notify call.
Notify	Say	Allows you to play a message, using text to speech, on a Notify call.
Notify	Forward to notify client	Connects a phone call to a Notify WebRTC client.
Notify	Call	Makes outbound phone calls using a Notify workflow.
Notify	Join conference call	Connects an incoming or outgoing call to a Notify conference call.
Notify	Send SMS	Allows you to send short text messages using Notify to users' phones.
Notify	Queue	Places an active Notify call in a queue.

Parallel Flow Launcher

Launches multiple subflows in parallel.

A few things;

You MUST specify a count, without it, you'll get an error.
If you want to get an output from a subflow, in hte Flow complete
script you can access it via flow.output
flow.output requires the subflow has Return activity.

Branch

The offical use of this is "Splits the workflow into multiple transition
paths from a single activity."

I like to use this to keep my lines clean.

Join

Unites multiple execution paths into one transition.

Generally I remove the "incomplete" transistion off of the activity.
Also, ALL activities connecting TO this must complete.

Return Value

Returns a value to a parent workflow, when run from a subflow.

Run Script

Runs the specified script in the scope of the workflow version.

This activity is ver versitile. You can add transisitions based on
values you set in the scratchpad and then have those go off. This is a
great replacement for;

Attachment Note
Soap Message Legacy
Rest Message Legacy
REST web service
SOAP web service

Set Values

Sets values on the current record when the workflow quiesces or ends.

If

Checks a condition or script to determine if a Yes or No transition
should be taken.

Approval Action

Performs an approval action on the current task.

Approval Coordinator

Creates an approval whose outcome depends on the outcome of one or more
child activities.

Approval - Group

Creates approval records for each member of a specified group.

Approval - User

Creates one or more individual user approvals.

Manual Approvals

Watches and manages any approvals that users add manually outside of the
workflow process.

Catalog Task

Creates a service catalog task record. These records are associated to
the workflow via the wf_activity field.

Create Task

Generates a record on any of the tables that extend Task [task]. These
records are associated to the workflow via the wf_activity field.

SLA Percentage Timer

Pauses the workflow for a duration equal to a percentage of an SLA.

Timer

Pauses the workflow for a specified period of time.

This should be added to the begininng of every workflow to have the
workflow run on it's own thread.

Create Event

Adds an event to the event queue, but does not immediately fire the
event.

Script

initialize

Method called by the Prototype JavaScript Framework during object
construction.

startFlow

(workflowId, current, operation, vars) Starts a specified workflow.

startFlowFromContextInsert

(context, operation) Helper method for business rule "Auto start on
context".

startFlowRetroactive

(workflowId, retroactiveMSecs, current, operation, vars, withSchedule)
Used by the "Start Workflow" business rule on table task_sla to start a
workflow. ## runFlows

(record, operation) Runs all workflows for a given record in a given
table and its descendant tables. ## getReturnValue

(workflowId) Gets the appropriate workflow return value for the input
workflow ID. ## getVersion

(workflowId) Gets the appropriate workflow version for the input
workflow ID. ## getVersionFromName

(workflowName) Gets the appropriate workflow version for the input
workflow name. ## getWorkflowFromName

(workflowName) Gets the appropriate workflow for the input workflow
name. ## hasWorkflow

(record) Determines if a specified record has an associated workflow.
## fireEvent

(eventRecord, eventName) Fires the named event on the input record. ##
fireEventById

(eventRecordId, eventName) Fires the named event on the record specified
by record ID. ## broadcastEvent

(contextId, eventName) Broadcasts the named event for the specified
context ID. ## cancel

(record) Cancels any running workflows for the document.