Know a little about the person first so you can plan something they will be interested in. I suggest chatting with them online or make them a Facebook friend (if you have never met them). You can always go old school and talk on the phone. You want to find out some of their interests and what they have already done. Something new and exciting is always a way to ensure a great first date.
Everyone usually likes to eat so I would suggest dinner or a drink with appetizers. Pick a place that has a variety on the menu. I find that the majority of people love mexican food places and their drink specials. The bar area tends to get loud so allow time to get a table if you plan to have a conversation.
Date activities should make both people comfortable. It can be as simple as getting dessert or coffee after dinner or seeing a live band. Live bands are always fun and you have time to talk between sets. Movies limit your conversation time. More active options would be walking up Mt. Bonnell, strolling around Town Lake, renting kayaks, etc. A drive out by Lake Travis to enjoy the sunset is a very romantic idea for dates.
I hope you find some of these ideas helpful.