Positive self talk. Reframe every negative thought you have about anything (Yourself, your life, your game) into something positive (ive found since ive been doing this I can find a positive angle on almost anything that happens to me).
While you are sitting on the train to work think to yourself "I like my self, I like my life, I am attractive, its easy to meet women/men ect ect". Try to beleive it while you think it, If you have trouble believing it at first while your thinking about it remember one time when it was true e.g one night when you where feeling confident, one girl who was really attracted to you. Do this through consciouse effort with the goal of vrouwen versieren until it becomes habbit.
Dont complain or say anything bad about anything or anyone unless it will acheive something e.g if someone is being rude to you, then you might need to say something negative to assert yourself.
Although there are dozens of visualisation and self hypnosis exercises which work as well they take time and commitment whereas positive self talk is something that you can do all the time. Read "what to say when you talk to yourself" Which ive found super useful.