Keep it short. Your CV should fit on one or two sheets of A4, so write concisely and be shrewd about cutting fluff. The chairman of a bank will be too busy to care about your GCSE in woodwork.
Know your audience. If you're applying for a variety of jobs, don't send a generic CV - talk up the skills that pertain to the post. Summer jobs and university activities smack of desperation, unless you're a first jobber.
Don't lie. Fabricate your degree and you risk losing any job you might land - as happened to NHS executive Neil Taylor in August. But let employers infer shortcomings - don't help them by stating anything negative.