Finally, contact journalists or public interest groups that have interest in your topic. Doing your research first will inform you as to the key events and key decision makers on your topic, help you pinpoint documents and agencies in your requests, and keep you from requesting material extraneous to your interest. If you don't do your research, you won't have any reference points for making your FOIA requests, and they probably won't bear much fruit. Don't file frivolous requests, either. FOI offices are already overburdened enough with specific requests that will eventually provide significant information.
Many agencies perform computerized searches for documents, so use keywords and phrases.
Also, provide accurate titles and dates, full names, et cetera. In other words, assist the person doing the search by providing key items of information. Don't write two-page supporting essays for your request, as they will only confuse the FOI officer. Send your request to the agency most likely to hold the records. While the Department of State and the CIA have one centralized FOIA office, the military branches, for example, have individual FOIA offices with each unit.