Plan ahead.
Read the requirements of the agency and draft an outline. You may have to register one month in advance.
For Internal Review:
Remember to have the grant to the grants office at least three weeks prior to the agency deadline.
Keep it focused and simple.
Your reviewer will not be as expert as you, so provide the needed background. The experiments proposed should address the hypothesis. Preliminary data that strengthen the proposal should always be included. Only propose what can reasonably be done in the granting period.