I started doing and achieving things I feel proud of. Advice like "just liek hav self esteem", "focus on the good things xd" are useless IMO, however well intentioned.
If you read a lot of books, say, Kafka's complete novels, you can say "hey, I knoe a lot about Kafka". If you ace a test, if you talk with a guy you like even for 10 seconds, if you make a painting, you can actually say " I made this", no self delusion.
In the end, thats what "esteeming" is about. Putting a value on things (yourself, in this case!)
Having enjoyable sex really helped my self esteem. Bad sex dd the opposite. Do you thing you can find a nice fellow, op?