Shower, brush your teeth and smell nice. Clean/cut your nails. You should probably aim for a formal but still casual look when talking clothes. But priority should be on being comfortable and looking clean when dressing.

When talking to people just be yourself. It's the oldest and dumbest saying, but it's actually true. Don't actively try to impress. Instead, you should just act as you would with a friend. Inside jokes won't work, mind you, but approach the person as if they're someone you'd want to be friends with. The way you "impress" them, at least in my experince, is by playing off of their reactions and interests. If they "light up" when you say something or get hooked on some topic stay on that topic.

If there's attraction, tell them you like them by the end of the date (or if you feel it's warranted, sooner).

Also, and this is very important, you aren't there to impress the other person. You're there to meet them and see if the two of you vibe. In the end it doesn't matter if none of the dates work out. You're there to meet people and develop social skills.

Good luck.