There is a saying in improv, "if you are in your head, you are dead". I am an introvert and spent my 20s in a mis-guided ways, trying to compensate for my introversion with self-pity, joining the pick-up community etc. Its crazy but in all fairness, first and foremost is that stop looking yourself as damaged goods and trust me, you would need experience but "better alone than in bad company". This is what I did to overcome my nagging short-comings,
1. Work-out/Recharge - get into shape, not above average but the best possible shape you can get into.
2. Read, as an introvert this should not be a big problem, but read classics, psychology, philosophy etc. stuff that is not technical and computer science. You will pick language, knowledge and wisdom from these books
3. Mediate - we live in a hyper world, and most of the loneliness and shyness comes from social anxiety, you need to relax - respond to the situation but not react.
Listen.. Listen.. Listen. Talk to those people whom you are willing to listen. Its much easy to engage when you can are willing to listen - most people think they should have something interesting to talk, but often it is that they are not interested to listen to the other person.
These are the things that helped me improve - am I an extrovert now? absolutely not, but I am content with whom I have become.