I'm a big fan of starting with exercise and letting the nutrition side follow.
Find something you enjoy and focus on being consistent at this point (at least 3 days of exercise for the first few weeks). Don't worry about the quality of the exercise or the duration when you're starting out, the most important thing is just to develop the 'habit' (then you can move on to bigger things).
If you do want to make changes to your diet, start with something simple (and sustainable) like smaller portions and eating out less. Diets are generally useless...It's all about sustainable lifestyle changes.