Self help, but especially CBT in general and CBT self-compassion worksheets in particular.CBT stops us from thinking: I always fail at relationships/my life goals/everything I do. It makes us stop and think: No, I have a good relationship with... I achieved ... When I ....it was a success.
Bit by bit you learn that what we actually do is dismiss or not celebrate what we are good at - we take it fgfor granted, and we focus on things to feel bad about. When we reverse that tendency, life is better.
A PP asked about small worlds - I don't know that quote but I do love Susan Jeffers' theory that you should have nine areas of life that you develop with equal attention and value. So prioritise your fitness and your friendships as much as your partner and your work etc; always have a contribution to the wider community on the go, as well as some hobby and some connection to nature. That way when life goes badly wrong - you split up with a loved one, or get fired from work or a house move falls through, you have all the other areas of life thriving and they keep you going. I taught this skill to DC and it helped both of them massively when they first had their hearts broken.
I also love Flylady's theory that you should love the home and body you are in. Even if you can't afford to update your home, you clean it and tidy it and arrange it in the best way you can, and give it focal points that give you pleasure - whether that's grouped photos of loved ones or a cheap vase of daffs on a sunny window etc. Caring for your home as if it were a palace is very therapeutic. Same with our bodies. Whether you are an ideal weight or not, take care of yourself as best you can with fresh air, exercise, healthy food, good hygiene, nicest best fitting clothes every day etc.
These feed self esteem.