1) Know the style of game your about to play in. A Private Investigator may not mess in a black ops game, a combat machine may not fit into the 'mission: impossible" style infiltration/subversion style game. Fit the style or your character will spend most his time waiting to do something
2) Have a theme/gimic somthing that makes your character stand out from a roleplaying perspective. Something not 'annoying', but gives your character a greater sense uniqueness. A quirk, a habit, a common phrase.
3) Specialise in some knowledge that will be useful on a semi-regular basis - be the Mafia expert, the ex-corper, the magic creature expert. Be an expert in something that will come into play... but don't specialise too much. And work with the GM on this one. Maybe hmm... 'Japanese Corps' or 'organised crime'.
4) Have a role in the team that is yours, and make that role something other then 'killing machine'. Whose the Face? Whose the Hacker/Technomance/IT systems guy?, whose the security systems/infiltration guy? Whose the magic master? Whose our driver? Then expand that role beyond the minimum. The driver could also be the drone expert, who also has contacts that speciliase in smuggling and fake SINs. The Face is also well connected, is also good at blending in at functions, etc. The Magic user has a combat spell or two, but can also assense, use ritual magic to track targets etc. Try mix and matching, the magic user whose spells are all 'face' type or 'infiltration' type.
5) Roleplay your character. Make something that you will actual roleplay. Don't spend all session min/maxing your character and telling everyone how cool your character is.
Show us how cool your character is.6) Feel free to use your favourite tv/movie/game character, but then make it your own. Most 'heroes' are solo players, you need to make your character a team player. Use the inspiration from whereever it comes, but then make it fit the game and the
team7) Have a background story with hooks. Don't overburden your character with every possible trageity, but give your character some.. character. Have family, friends, ex-loves, enemies, rivals. Have a reason to be a runner other then 'i need the cash'. Have an end goal, anything from ' I want to open a gun shop' to 'I want to make megacorp X pay for firing me!'. Gives you something to work towards and gives your GM something to make the missions more interesting

Have at least some ability in the following: Firearms, unarmed combat, dodge, perception. Nothing worse then the Troll, whose great with longarms and machine guns, prove to have no skills in pistols or unarmed combat.
9)carry a backup weapon... just in case. Something small and concealable, maybe ceramic.
10) Have as many contacts as possible, and flesh them out for the GM
11) Have as many SINS as possible. Perpare to loose a few.
12) Have licenses for your weapons, but don't expect a licence to fly when you walk down the street with your SMG swinging at your hip. KE aren't that slow.
13)Be ready to remake your character. Its only through game play that you find out how your character works. What seems good on paper may prove to work differently during the run.
14) Have fun, its the golden rule!
