Um.
Avoid silver and iron.
Bow and scrape to anything more powerful than you (afrits, marids, and certain named spirits).
Staying in one shape too long hurts, so shapechange periodically.
Water bad, earth bad, because we're associated with fire and air.
If we find out our summoner's true name we can do basically whatever the hell we want with her, since she can't inflict magical punishments on us without us turning them back on her, and it's implied that if we spread her name she'd probably be torn to bits while crossing the marketplace Abdul Alhazared style.
Treat any spirits lower than you (imps, foliots) with a certain measure of disdain and don't be afraid to bully them.
I'll probably come up with more info as the game progresses.
Also don't fuck with Solomon because he has a functional omnipotent in his ring.
Oh! Spirit rankings. Top is most powerful, bottom is least.
Above marids: warp reality just by being there. If we try fighting them we lose period; if we even go near some of them we die. Examples: Spirit of the Ring from Solomon's ring: can do pretty much anything (summon an army of 50,000 marids, give complete magic immunity, hurts the wearer's soul just by being there - and he'd be more powerful unbound).
Marids: pretty fucking powerful. The Titan Atlas was one of these, charged with holding up the Parthaneon for doing a shit job at construction. They exude so much magic it lingers in the air behind them, leaving a trail for those who know how to see. If we tried to fight one we'd die, period.
Afrits: bigger, more badass djinn. The most powerful commonly summoned type of spirit (marids take 2 magicians to summon successfully). If we fought one we'd likely die.
Djinn: the all-rounders. Pretty powerful (enough to catch a small building to the face and throw it right back at their attacker), but more resourceful due to their lack of godlike power. They can range in power within their class, but is think we're about the middle.
Foliots: they're basically the mooks of the spirits. Commonly used, get stomped on by anything above the, but fairly capable. They know how to bow and scrape, though.
Imps: these guys are basically only good for spying and delivering messages and stuff.
Below imps: these are stuff like spirit hornets and such.
http://en.wikipedia.org/wiki/Bartimaeus_Sequence