First, you have to enjoy it. It’s rare that someone sticks with an exercise program that they really don’t like, let alone gain lasting results. I’ve never met anyone in good shape who hates the exercises they’ve done to get there. It’s absolutely key that you find things that make you happy. If you dislike the atmosphere in a big gym, don’t go to one. Try going to a smaller fitness studio, or put together an at-home gym. If running is boring to you, find something that’s more engaging. I find what my clients enjoy and incorporate those things into their prescribed exercise program.