Firstly and most importantly you must maintain a conviction not to listen to naysayers who try to convince you not to do your avodas hashem.
Step two is you just do it.
There is a guy who used to work in my school who went from really overweight to really not really fast. The story is told that he had a conversation with his wife where she spoke of the hard ships of losing weight so he told her it wasn’t that hard and just to prove it he did it.
So the answer is don’t do diets, Just lose weight. Just do it. Forget lifestyle changes. Forget rules.
Eat Healthy (Foods). Eat little. Early in the day. Oh, right and exercise. A lot.
I think the main thing to keep in mind is to stay away from the people who think dieting should be done in a healthy way. Seriously. A tiny bit of logic aught to help you. People who eat healthy don’t lose weight. If they did people would just disappear into nothingness by eating healthy. But they don’t. Healthy people stay the same weight. If you want to lose weight you have to do something unhealthy.