Create a FOIA "Campaign", Not Just a Request
Attaining information through FOIA is not always the short process as many imagine it. Often times one request simply will not secure the information requested or will leave out helpful records. Instead, a prolonged strategic effort may be required in order to secure the greatest amount of information. Success often mandates a series of well thought out requests and litigation instead of one "catch all" request. For this reason, thinking of FOIA in terms of the creation of a campaign instead of an individual request may assist in attaining the information you are seeking.
A very strategic approach to FOIA will provide you with the best results. Submitting one general request that asks for "everything" may not secure you anything, especially when you are seeking information that the government does not want to disclose. Instead, start with what you do know. Is there a document or communication that you are confident exists? Try asking for it and no more. From there use information in that document to request other information you know or have reason to know exists. Think of the government as a dam and the information they are withholding as a massive amount of water behind it. Your goal is to create a deluge. To do this, start with a small breach. From there you can leverage the small breach to create a larger one. After a prolonged effort, you will have a greater chance of creating the flood of information you were aiming for.
Be Prepared to Litigate
If somewhere along the line there are denials to your requests, including your appeals, you should be prepared to litigate the issues in federal court. Most requesters of information simply quit after a denial. Rest assured that the government knows this. Litigation may get the government to comply outright. If not, the judge may rule in your favor, deeming the information improperly withheld, granting you the right to have it. While you can litigate FOIA denials without a lawyer, it may be best to hire one. Litigation is often long and complex. If you are successful in attaining the requested information through litigation after a denial by a government agency you may be entitled to attorney fees.