The best way to improve your writing skills quickly is to read good literature. Once you know exactly what is correct/sounds correct, then you will know when something is wrong, even if you don't know why. I know many people who can tell you all the parts of speech etc. but still make simple grammar mistakes. It's better to learn through exposure. Knowing whether something is correct is better than knowing what makes it correct. Any books that are generally considered to be well written should work. Though, I would avoid Edgar Allen Poe. He has an incredible vocabulary...but his writing might be a difficult read for someone who is still learning.

You can't learn a language fast. Write in the italki Notebook every day and make a list of your common mistakes after you see the corrections. Then try to overcome them.

Write every letter repeatedly. Do a simple excercise 20 A's, 20 B's 20 C's etc. Use http://www.kidzone.ws/cursive/index.htm to practise