Hi there, a lot of play-by-post games are pretty newb friendly -- most PbP is much more role play than dice rolling anyway. That said, there hasn't been much PbP on these forums for a while (there was a stretch with a lot of down time for this site, so games mostly migrated to other platforms). I might suggest checking out RPGcrossing, which is a large community of PbP for all sorts of game systems including ShadowRun.
As for PbP etiquette
- The biggest thing is not controlling other players' characters (for example, you don't write "My character 'Able' and Bob's character 'Blaster' lay down suppression fire." Instead something more like ,"My character 'Able' lays down suppression fire, and calls out to Blaster 'Keep them from coming through the door'." (and ask other players, don't tell them, and for that matter most of that should happen 'in character' (IC) rather than in out of character (OOC) conversation
- Generally working with what others have posted, even if you don't agree that it is the best course of action. A one hint on this guideline is to look up the 'rules' of doing Improv and sort of translate those.
- Not everyone will have the same posting schedule: be patient! But try to post regularly yourself.
Good luck finding a game, and hey maybe I'll see you at a virtual table one of these days.