Help and guidance can be provided to the user in a number of complimentary ways:
Captions
Can be applied to list and tree views of records.  This can be used to inform the user about
the list they are currently viewing and what they might do next.
Can be applied to edit forms to guide the user in what to do.
Can be applied to individual fields, to provide additional guidance for that particular item
Context sensitive help
Context sensitive help can be used to provide the user with additional instructions to help complete a form.
Pop up help
Pop up help can be used to provide additional information to the with relationship to specific fields. 
The image below shows an example of some pop up help.
Mandatory fields
On an edit form, to help the ease of use, all mandatory fields are coloured blue (by default), whilst other fields are displayed in black.
This enables a user to quickly become familar with any data entry screen and focus on the mandatory fields which need to be populated.
The image below shows an edit form which contains an picture and a caption informing the user what to do. 
A field caption is also used for the User id field and the Name field is shown in blue as it is mandatory.