Clarity, simplicity, brevity. For state and federal programs, you'll probably have to use the jargon they used in the RFP, for foundations and corporation grant programs, use plain language and define any specialized terminology you can't avoid using. Include all documents requested in the guidelines. Make sure your budget makes sense. Explain any apparent peculiarities in it.
Discretion is the better part of valor.
Whenever government funds are being used to enhance the capacity of the organization to fulfill its mission, certain guidelines could be followed to minimize external government interference in the internal affairs of the agency. Whenever funding exceeds this amount the potential for interference increases. Keep all reporting forms current. Ensure that the mission of the organization drives the demand for funding, not the other way around. Individuals in this field are often called social entrepreneurs.