Step 1: Work on yourself.

Physically - Go to the gym, eat right, increase your stamina

Mentally - Read, be in control of your emotions, be present, learn to overcome your fears and insecurities

Step 2: Go out and socialize.

Sure staying at home is comfortable, but you won't improve this area of your life. Be a yes man, go out and socialize when you can (a healthy amount obviously)

Step 3: Learn from your awkward interactions.

I've learned more from the interactions that didn't go well than from the interactions that went smoothly. The path of least resistance won't teach you that much. If you only have good interactions you'll be kidding yourself for down the line when it can get pretty awkward, and if you haven't dealt with that much, you'll panic and leave.

Do this and you'll never have to worry about 'what do i say' again.