How do I write dialogue?

I've been told by a few people that I'm good at writing dialogue, and I believe I've realized why this is. Now, I might not be great at creating clearly distinctive personalities through speaking style or vocabulary, but I try and it works a bit, as far as I know. I haven't gotten definitive feedback on that part yet.

The realization was that I've always thought and imagined conversations in advance in my head in real life when I need to talk, because talking doesn't come very naturally to me. I detailedly go through what I need to say so that I don't have to stammer and slow down when speaking. Also, since speaking is hard for me, I've had to choose words, word shortenings (in Finnish) and sentence structures that are easy to say, making speech sound more like speech than text. It is a bit surprising that it has worked in English for me as well.
Too bad that my careful planning only works for the first few things that I'll say because I royally suck at guessing what the other person will say.

Well well, having symptoms of Asperger syndrome isn't all that bad.