Going back to basics while you figure out what to do next is very common. Don't worry about it. I used to do that all the time. As you dance more, you'll learn more precedes and follows and have more choices of what to dance after each figure. Then you won't have to go back to basics all the time because you can pick from a few other good following figures. That's basically just knowing what you can do and then practicing them, using the different follows instead of the same one all the time.
I don't know about lindy, but improvising in general usually isn't easy. It's a separate skill in itself. I don't think I can give you tips for that. But I would suggest making sure you have a good grasp of the basics and theory, how steps and figures fit together and why they work in some combinations and not others, that sort of thing. If you really know how the dance is structured and why, then you should be in a much better position to play around with it and do things outside of the standard figures while making them look good (and not like you're just fudging things to get by).
It's hard to tell you how to have fun and enjoy yourself. If you think you're worrying too much, then try not to. Easier said than done, I know. But mistakes are going to happen, you'll bump into couples, miss a lead or something. Give a quick apology if you want (you don't have to do it for every single little slip though) then let it go. Smile (in general) and sort of laugh it off. Try to relax a bit and remember that even if you're trying to do everything correct with great technique and all that, it's still supposed to be enjoyable. Do your best, but don't let trying to be as correct as possible get in the way of enjoying the dance. Having more figures to dance can help, sure, but it's not all there is. If you can dance a few figures well, that's often better than dancing a lot of figures poorly. To help keep things interesting, try to mix up the steps a lot and not do them in the same order all the time. That might not be easy, but try. Think about what figures can precede and follow each other and mix them up when you dance. Maybe chat with your partner a little bit. When you go into a basic step, it hardly takes much thought to dance, right? Well, you can use that time during a basic for something else. Thinking of what you'll do next is one, but you can also have a quick exchange with your partner. And that could be anything, a "how are you", a compliment on a move that was lead/followed well, whatever. You can also try to work off your partner. I find that I usually enjoy a dance more if my partner's into it a bit, giving me some energy and a good connection to work off of. If she's enjoying it, I'll enjoy it more, too.
Hmm, I could probably think of some more if I tried, but that's mainly what's coming to mind right now. I'm not sure if that's of much help or not, but I hope it's of some use to you. Good luck.
