Field Names

Labels: Refer to user interface elements using the element's exact label (including any end punctuation, such as an ellipsis). For example: Click Add... to browse for files on your local computer.
Capitalization: Use title-style capitalization for field names. Don't capitalize field when used as part of a name, unless in a heading or considered part of the proper name. For example: Import your data into the Lead Source field.
Formatting: In documentation, field names display in a monospace font.; In user interface text, don't use special formatting when referring to field names.
Custom fields: When referring to a custom field that you recommend users create, use the same style conventions as when referring to a standard Salesforce field.
Prepositions: When referring to fields in relation to objects, use on instead of in. For example: When you create a custom field on a standard object, you must add the custom field to your package explicitly.
List fields in tables: When listing fields with descriptions, use a table. Don't use a bullet list or definition list.

Salesforce Style Guide for Documentation and User Interface Text