Well, in terms of etiquette, a lot of things vary from player to player and group to group. There really aren't a lot of hard and fast standards. For example, I actually never have a "can't post again until everyone else has posted" expectation in my games, and I haven't played a whole lot of other people's games that did either... but some do! Because of that, the most important thing is to read an RP's rules. If they're written well, they should give you a basic understanding of the RP's expectations.
There are a few other things you can extend beyond the scope of one game, though -- basics, really. Let the group know if you can't post for an extended period of time or if you have to withdraw your character. Don't metagame (use out-of-character information in-character). Don't control another player's character without permission from the player. Don't godmode (which can be lots of things and vary slightly in its definition, as discussed in
this thread, but my basic definition is "acting in a way that makes your character not subject to rules and logic that should apply to everyone in order to get an unfair advantage"). Those are the most universal things I can think of.
In terms of searching, I usually change the post order to newest and browse the most recently-added games to see if anything catches my eye; if I'm using tags, I find setting the post order to newest or activity is even more important. Nothing is less fun than finding an RP you think would be just perfect and realizing it never got off the ground and hasn't been touched in half a year. xD You can also filter
out tags you don't like. If there's anything you're looking to avoid, go to the roleplay tab. Click on the link to manage your filters and sort method. Type what you want to ignore in the ignore box, and you won't see those games. There's also a highlight box where you can put tags you're especially interested in, and it'll highlight those games for you.
(As an aside, every time I see someone on this site complain about high school RPs, I get the urge to go make one. :P)