Make sure you know the rules. During school terms you can't work for more than 2 hours on any day except Saturday, when you can work for up to 8 hours. However the total amount of work you do during a week can't exceed 12 hours. You also can't work for more than 1 hour before school or at all after 7pm
Wherever you work (even if it's during the school holidays) your employer must obtain a permit from your local education authority. (That permit can be withdrawn if your teachers believe that your employment is interfering with your school work).
http://www.direct.gov...entsRights/DG_4002945
You won't be able to commence full-time work until after your school-leaving date, which (assuming that you're in England) is Friday 24th June 2011.
Very few jobs for young people are ever advertised and many employers won't accept young workers because of insurance problems. So it's going to be an uphill task finding a job. The usual places to try are hairdressers (popular with girls, less so with boys), independent shops, local cafés and market traders.
It's also worth remembering that the cumbersome rules on employment don't apply if you're self-employed. (I remember reading about an 8-year-old boy who was running thriving antiques business!). Ironing, car-washing and dog-walking are all ways of running your own business.
Chris