The majority of grants require, first and foremost, that you complete a full-length feature screenplay. Different grants award money for different genres, so be sure that your script is within the parameters of the specific grant. Grants are available for novice screenwriters and for experienced professionals for un-produced, unpublished, un-optioned work. Typically, you can apply with a writing partner, if you have one, but the money is split between the two of you, not doubled.
Any of the following may be required additionally along with your grant submission application: fees, letters of recommendation, resume, letter of intent and a curriculum vitae. Compile the additional material in a professional manner, taking care to have everything properly formatted and checked for spelling and grammar. Nothing looks worse on a screenwriting application than obvious, elementary writing errors. Also, pay attention to restrictions such as not having earned over a certain amount as a professional writer, that would prohibit you from being awarded the grant.
Some of the most prominent screenwriting grants include the Nicholls Fellowship ($30,000), the San Francisco Film Society Grant ($35,000), and the Hearst Screenwriting Grant ($15,000). Information for each of these grants such as submission information, deadlines and past winners can be found online at their respective Web sites.