My BIGGEST motivation was being diagnosed with cancer 2 years ago and wanting to become as healthy as possible for my husband and 2 kids.
I signed-up for a 1/2 marathon (I'm not a natural runner and haven't run in almost 7 years). A local running shoe store had a program that you could enroll in to train, and you really have to follow it to do well in the race.
Now that it's done, there are more excuses and reasons for not running as often. Believe it or not, I didn't lose a lot of weight, but I changed my body by replacing all the fat with lean body mass (muscle).
The BIGGEST thing you can do is to be more aware of what you eat and how you eat it. It takes the stomach 20 minutes to register fullness. Most of us eat WAY more quickly than that and over eat as a result. I know I do. Drinking a glass of water before meals is recommended to help fill you up and to prevent over eating.
However, there are some hormones that play a critical role in weight and may be out of balance (though most have NO tests to diagnose the imbalance or treatments to fix them). Hormones that can effect your weight include but are not limited to: insulin, cortisol, ghrelin, leptin, amylin, GLP-1, thyroid.
Almost universally, people agree that Weight Watchers (my husband's doing the online version for time considerations) is the best, most balanced way to lose weight and be accountable to it.
GOOD LUCK!