If you change everything immediately, you are going to crave things and over eat. Do this in a slow process. Remember that you are aiming for a permanent change, not a quick fix.
Don't try to drop weight quickly. Your body resists quick weight loss and tries to retain its stored fat. Trick your body into losing the weight by doing it gradually.
Don't starve yourself because if you do so your body will become tired and will not function properly.
Beware of foods selling themselves as "diet" or "healthy" choices. The packaging will often tell you some good news (low fat!) and ignore some very bad news (incredibly high sugar!). When in doubt, nothing is better than an apple.
When exercising for the first time, don't overdo it. If you put too much pressure on yourself right away, you risk burning out or even injuring yourself. You're much more likely to keep up healthy habits if you work