For me, self esteem came with success. Set little goals for yourself of things you genuinely want to do and getting them done will make you feel better and give you experiences you can point to in the future when things are difficult to show you can do it (whatever it is).

Experiment; if you want to feel better around other people, decide to greet 1-5-10 people and you'll be gleeful :-) and get an attitude, "Look at me, I said "hello" to 4 strangers and they smiled and said "hello" back!" Being gleeful at such little things will make you smile at yourself and realize it's okay to be shy and anxious and you are actually sweet and everything will be okay, it will just take some time and practice.