the only successful foia is the one that you do not make...
the one that you make, but only after acquiring a hard-copy of the data you seek prior to making it. that way, when feds say, we don't have it, parts are missing, or they just white out 99% of the document, you can pull out the ace up the sleeve and blammo: you can prove it with cold, hard evidence.
but you really have no chance at a "successful" request. feds have proven time and time again that they will fight tooth and nail, over the most miniscule, arbitrary details, to prevent you from accomplishing your mission(s).
its actually set up to be intimidating, as the feds view anyone asking for data as an adversary. of course that's not what they say, but its overwhelmingly obvious to all peoples interacting that someone does not like being asked anything about their job. that you pay for. and they do not like being asked to do their job (that you still pay for) even more. i'm being snarky, but that is reality. there's a bunch of stories where feds acted unjust/illegally in regards to foia, but my favorite just happened, after the naval yard shooting in dc (i think the beginning of 2014), where a journalist foia'd some info, and the navy's foia point woman, literally her job to handle foia's, writes out her plan to avoid and elude the reporter's questions for as long as she can....she's writing to her peers for advice, thoughts, etc., on how to avoid doing her job, and avoid giving you, the american tax payer, that makes all of this possible, the request that you have every legal right to have.
so smart foia lady cc's the reporter on the email, which he naturally publishes.
there is no formula for how to overcome that...corruption, deceit, sloth, pathetic displays of character, etc., whatever you want to call it...it's what we are facing when we foia: the other side is actively working against you, regardless of what they say to you, or anyone else.
another thought: define success...i'm sure we have very similiar goals/agendas/etc., but what you deem a success, i may not. that's just life. for example: no foia for nsa/snowden/prism will be successful in my opinion until we have the chats between the nsa and microsoft, google, etc., where they are talking about how they are going to spy on us, while destroying the constitution. but that's my definition of success....idk what yours is.
i do like the question, just don't think there's any methodical way to make them successful; when the system is stacked against you, sometimes the best play is to not play...