A good fitness workout should last at least 30 minutes and encompass a range of aerobic, strength and cardiovascular fitness training.
Varying your fitness workout from week to week will help keep you motivated and interested. Trying new sports - is a great way to maintain your interest and your fitness levels. Playing a team sport will give you a very good reason to get and stay fit and also plenty of people to train with (and it's great fun as well!)
Speak to a personal trainer to get a fitness workout developed specifically for you. A personal trainer will be able to take into account what you enjoy doing and what you don't enjoy and put together a program to ensure you get the most out of your efforts whilst staying motivated and enjoying yourself.