When writing status bar messages, begin the text with a verb in the present tense and use familiar terms — avoiding jargon. For example, say "Cuts the selection and puts it on the Clipboard." Try to be as brief as possible so the text can be easily read, but avoid truncation.
Be constructive, not just descriptive, informing the user about the purpose of the command. When describing a command with a specific function, use words specific to the command. If the scope of the command has multiple functions, try to summarize. For example, say "Contains commands for editing and formatting your document."
When defining messages for your menu and toolbar buttons, don't forget their unavailable, or disabled, state. Provide an appropriate message to explain why the item is not currently available. For example, when the user selects a disabled Cut command you could display "This command is not available because no text is selected."