Good question, but definitely not a easy one to answer. A lot of it really comes down to being able to "love yourself". Basically the reason people seek external validation is because they feel a deep lack and subconsciously feel that if enough people approve of them then that lack will go away. The goal is to make a conscious and subconscious shift to valuing your own validation above others. So for example if you bang a chick much hotter then you already have, you care more about the inner feelings of happiness rather then bragging to your friends. You simply feel content with your own approval

How do you make this shift happen? It's not easy, but a good place to start is to completely cut off all bragging and telling people about your "victories", atleast for a few months. This will completely starve your subconscious of external validation and force your brain to look elsewhere, which will be hopefullly inwards. Also, becoming very goal oriented is another good step. Consistently setting goals for yourself that you then accomplish will give you a sense of pride and inner fulfillment. Consistently doing that will give you a sense of inner accomplishment. Lastly, I recommend avoiding measurement of yourself by anyone elses standard other than your own. This means that if your parents think it's important for you to have a high salary, but you think it's more important to do what you love you don't let there standard dictate how you feel about yourself. PS banging a lot of hoes will also help :)