Find a hobby you enjoy and do that. Also, fix any obvious flaws, such as poor dress, being out of shape, persnonal hygiene, etc. lastly, practice small talk: when at a store, make a comment to the clerk, try to make them smile, etc

The goal is basically improve socialization skills (small talk), remove frictin to friendships (hygiene, fitness, fashion), and then put yourself in situations where you meet people (hobbies).

A local couchsuefing group can also be good, if you staet couchsurfing hosting.