I've found that trying to give up something completely just leads to cravings and thinking about it all the time - curtailing my intake to a small number is easier, particularly if I say 'I can have x or y or z, and right now I choose x' (or choose to wait and have y later).

At the risk of repeating the obvious: exercising makes you heavier, because muscle is heavier than fat. It also makes you healthier and more flexible (thus less likely to injure yourself) and puts you in a better mood and all that... but it's not an effective weight loss thing. (For me, cutting carbs was, but that's because my metabolism is wonky.)

I feel guilty about taking time away from work for hobbies - like climbing or martial arts, where I might see other people.

Learn from my mistakes: looking after yourself is not an optional extra. If meeting other people keeps your spirits up, you need to do those things.