The most important thing for making shadowrun characters is to define the charcter before putting pen to paper in any mechanical way. What is the character good at? What is their role in the group? What mechanical elements do they need (skills, powers, spells, implants, whatever) to fill that role? If you are building 400 point characters you can end up with people with elite skill, but you can't be a one man army. Discourage generalists, and encourage people to know what they want when they start. Help them pick the things that are core to filling out their character concept, buy them first, and then fill in the rest with remaining points.
Also, set out some guidelines about power levels and dice pools, and stats. Try to keep people roughly in the same neighborhood in terms of dicepools. Are you expecting min/maxed characters who have an 18+ dice pool in their primary skill, or is a 14 or 15 enough for your core compentency? Are dumpstats of 1 acceptable, or do you consider a 1 vastly undeveloped and a huge weakness? Either standard is fine, but what you don't want is the combat specalist who has 13 dice with his best attack next to the face who has 14 with his combat secondary focus.
Please note, the sample characters in the book are crap, for the most part. I would not suggest using them as examples or pre-made characters.
Umaro's link above goes to some characters he made as sample characters for Missions games. They are at the other end of the scale from the sample characters is SR4A. While there is much to be learned from studying them in terms of technique, they are highly, highly optimized. Not a complaint or criticism, but know what you are getting. They were designed to let a new player sit in and be effective next to experienced players with experienced characters. Even if they exceed the power level of the campaign you are considering they are helpful for looking at good ways to put together armor, comlinks, etc.
