Start small. Simple things like just saying hello and asking how their day is going will help you ease into a conversation. Although it may be uncomfortable initially just push yourself to be more sociable eventually it will come naturally.
Instead of having friends in one category, try having friends in many. You don't have to take one big step and start out immediately. Start out small, greet people, if your a funny person then start cracking some jokes. Try hanging out with people that make you feel comfortable, if they don't make you feel comfortable then that's a sign that they are just meant to be acquaintances.