Eliminate or drastically reduce sugar from your diet. Cut out candy, cookies, sugary cereal, pastries, soda, soft drinks, sweetened creamer, etc. If you have to have sweets or soda, go for the sugar-free varieties. I know that aspartame and saccharin are bad for you. But if you are obese and sugar is one of your main culprits, the obesity will kill you before the artificial sweeteners will (in my opinion). This is just the first stepping stone. Take it one step at a time.
What I did at first when I eliminated sugar was I bought sugar-free varieties
of ice cream, cookies, cereal, soda, and drink mixes. I made sure that I didn't
eat extra amounts than I normally would just because there were less calories.
That is important. Now I don't even buy these type of treats at all. I opt for fruit when I want something sweet to eat. Sometimes on a "free" day, I might indulge and have a regular brownie or a piece of cake or some other treat. I try to limit it to one day a week.
Stevia is a great sweetener to use in coffee and tea. You don't even have to go to a health food store to get it anymore. Walmart now sells it and has a generic version.