Improving my writing?

Reading.

Even moreso than writing, reading is important because it will show you How It's Done. It'll beef up your vocabulary in a meaningful way (versus just memorizing words), it'll show you good ways to structure a phrase, it'll give you ideas, and so on. Another important aspect of it is that you can't learn to be a good or decent writer by reading about how to write - or to put it another way, the more "primary sources" you have, the better your own writing is going to be. The reason why most of the good science-fiction authors were good is because they were all scientists or at least, near the sciences so they could draw on first-hand knowledge. Whereas now, far too many sci-fi authors are authors first. 

And then of course writing. Shoot for X number of words a day. 

Most importantly, you just gotta start writing. It doesn't matter if what you think what you're writing is bad or if you don't like it or if it doesn't make sense or anything else like that. Just keep writing anyway. I know it sucks, but honestly you won't get any better at anything unless you practice. The more you write, the more you'll realize what sounds good and what doesn't. 

Also, like argentAegis said, reading is very important. Read what you like to read, read what you don't like to read, read everything. You'll get a feel for different styles and how the authors you like write. It will help you to develop an inner voice, which you can then use to your advantage when writing your own pieces. 

And when in doubt, I know it's scary, but let someone else read your work. You're reading it more than anyone, so more than likely you're gonna end up thinking it's bad when it's really not. Show someone. It's probably not as bad as you think, and if it is, you'll get some feedback. 

Don't give up, you'll get to a place where you enjoy your writing soon! Good luck :)