How many times have you vowed to clean up your act for the New Year, only to break most of your resolutions by the end of the first week in January? If you try to get thin, super-fit and give up everything you like all at once, you will need to be superhuman to succeed. The key to successful resolutions is setting achievable goals rather than making promises you can't keep. Want to make some New Year's resolutions you'll actually manage to keep? Read on…