I've talked a lot before about the need for communication in BDSM and in relationships in general, but for the longest time I had trouble doing it honestly. Because the advice is usually "ask for what you want," but I didn't always know what I wanted, and I felt like that rendered me unable to communicate. It's one thing to say "I like thuddy impact especially on my shoulders and upper back and I'll be cooperative but not submissive in my role"; but if all you can put together is that you think you'd like kinky stuff and to be on the bottom and for it to be sexy and you don't really know exactly what that means, what do you say?
The answer is "I think I'd like kinky stuff and to be on the bottom and for it to be sexy, but I don't really know exactly what that means." It's okay. Better than bluffing like you're experienced, better than mumbling into your hands--simply say what you're thinking even when it isn't totally clear and coherent. That's what really helps a partner work with you.
(In kink, talking about how you'd like to feel--"I'd like to be a little afraid," "I'd like to feel totally under your control," "I only want the physical sensations,"--can also help. It's not a replacement for explicit negotiation, because different things scare different people, but it starts the "well, what makes you afraid?" conversation.)
This goes for relationship stuff too. When someone says "Where do you think this relationship has going?" there's no need to try and make up something that sounds sensitive (or to cannonball out the window, do a shoulder roll, and run down the street screaming). If you haven't thought about it, "you know, I haven't given that enough thought yet, but I do love/like you a lot" is the answer that can start an honest conversation.
I know this sounds incredibly obvious, but it took me a long time to learn how to say "I don't know" gracefully and while still providing as much information as I do know. Communication doesn't mean saying the right things. It means saying what you're really thinking.