Well, I can tell you the most profound (but simple) advice anyone ever gave me was: You lose weight with diet, you get fit with exercise. And it's 100% true.
I had a medical obstacle that was hindering my weight loss- I have hypothyroidism- so one thing you should do before starting a weight loss effort is to see your doctor. A doctor can help with any medical issues and can monitor your diet and exercise to make sure you stay healthy.
The other thing is pick a plan you live with for life. Don't do these crazy diets that are unhealthy either in terms of the food/supplements you eat or the way they limit calories like crazy. Those diets are not healthy and they aren't sustainable. Pick a style of eating that focuses on healthy foods (limited meat, lots of vegetables, some fruit and grains). Understand that the American diet has way too many simple carbs- avoid processed foods like the plague and limit simple carbs like bread, potatoes, rice, and other grains- even whole grains. Focus on vegetables as your source of dietary carbs.
That's what works for me anyway. But 100 people will probably give you 100 answers.