If you decided to write a proposal, you need to learn basic information about the NSF itself. The National Science Foundation gives money for researchers in the majority of areas of science and engineering. Also, the NSF funds education for those who really need it. The Foundation is a government agency of the United States which has a great budget and funds near twenty percent of all research projects that is supported by the government of the United States. Moreover, there are some areas of science, such as mathematics, computer science, economics and the social sciences, which are funded by the NSF in most cases.
The National Science Foundation is structured and organized just like the universities are, with the exception that it doesn't have departments and colleges, and instead, there are divisions and directorates in it.
Once you learned about the Foundation, you need to get acquainted with the programs they offer. Then, it is necessary to look for the program that supports exactly your idea. Pay attention that there are many cases, when it is not really obvious which program is acceptable for your research idea. After you have chosen the proper program, you need to read its announcements and form direct questions that you would like to ask the program director. This is quite acceptable to send an email to him. At the same time, remember making your letter clear and coherent, identifying all the key points in your research. You may ask everything you want if it lies within the area of the program, unless it is not mentioned in the announcements.
Once you have clarified everything, it is time to write the grant proposal. The best way to do it is to follow a good-written sample.