Just look for things that you know you and your date will enjoy doing. And, if possible, have 2 or 3 things in schedule. Dinner, movie, walk in the park.. not necessarily those things, but you get the idea.
If you know the other person well, also try to think of things that might surprise him/her.
And finally, be yourself. Don't try too hard to impress the other person. Just be relaxed and act naturally.