Although AAA titles play in a complete different league, FPSC games have a similar miniture environment like the commercial studios - a lot of competition, need for innovation and a very discerningly "public". So imo some general rules apply for FPSC games as well as for pro titles:
1. Don't make announcements or promises you cannot hold (What I read from time to time in the WIP section in terms of self-delusion would make be burst out laughing if it weren't so sad). If you claim, your game will incluce "a stunning visual appearence", "REAL intelligent AI behaviour", " realistic and complex martial arts combat" or "a choice of starting characters each with an elaborate background", then you'll have to prove it sonner or later with screens, clips or demos.(p.e STALKER presented drivable vehicles during development and ditched them for the release of the game - which caused massive criticism and years later still everyone talks about it)
2: Only present stuff what will to 90% actually be in the game. Continuosly updates like "I completely rewrote the story", " I ditched the zombies" or "I decided to wait for CP's next segment pack to rebuild the space station from scratch" give the impression you have no real development plan. (p.e Tabula Rasa was designed as a Fantasy game and ended up as hard-core Science Fiction - it was one of the shortest-living MMOs in history)
3: The more often you provide an update on your game, the less you can afford to reaveal each time. If you can't update for a longer period, you have to provide some substational information or very juicy screens to make up for it. (p.e. AAA titles often present playable short-levels at conventions or to game magazines after a longer hiatus).
4: Be honest! Dont present screens with a wave of 40 zombies when your FPS was crawling at 4-6 when you took them. Don't "plant" moving decals, flying vehicles or driving cars into screens and claim they work as in a pro title. Don't say you "won't reveal the story yet and present it ingame in the first level" just because you have no freaking clue yet (and conveniently present lvl 2 later on instead of lvl 1). If during development you have troubles with something that is a key element of your game, then admit it and ask for help - this is one of the most helpfull communities I ever was part of.(p.e. professional game magazines keep brandishing "enhanced" screenshots or even refuse to do reviews based on demos they are not allowed to play on their own computers).
Hope that gives you some inspiration
In case you find my grammar and spelling weird ---> native German speaker ^^