Get yourself a trusty black trenchcoat or a pretty pink mohawk, make it your own, and live by it. Don't try to have a character that flip flops between seriously gritty and over the top excitement
Be able to do something in combat, something in legwork, and something logistically. A way to kill, a way to gather info, and a way to fix or buy items.
If you're going to serve up cheese to your GM night after night, expect him to send a cheese platter your way too (ex, if all you ever do is shock glove/shock frill and stick n shock, expect that to be met with someone with nonconductivity 6, a high willpower, and a 6 shooter full of rounds made to ruin your day)
If you turn out to be comically bad at your job, don't insist on playing it out to the bitter end, the end gets further and further away and more bitter the longer it takes.
Always have ALL of the basic matrix use programs. Your commlink can't do a damn thing without browse, edit, scan, analyze, etc. Might not even be able to take and receive calls if your GM's a dick about it.
Expect to be pulled out of your comfort zone. I don't mean just out of the van, I mean being forced to leave the van, and all the explosives behind to go spend a week in Africa (where your gnome will pick all sorts of fights for you). If you think you're going to live in a rigger cocoon, expect to be called to a court where they dojn't tolerate that monocycle with a valkyrie cocoon and make you stand about in the meat world, uncomfortably far from your rig.
Make something you'll enjoy playing, not something your GM or other players say they really need in their group.
If anything looks like the rule is too good to be true, try reading it from the perspective of an outsider. Negative qualities that are read as "optional negative qualities" aren't likely to be read that way by an outsider, and definitely won't be by the GM that finds out 3 sessions later that you've been ignoring the must in the rule for your guidance spirit from the beginning.
Forget about that black trenchcoat, wear a pink mohawk. Black trenchcoats are for silly WoD games and Top Secret. Go Pink, go big, go tusks.