How to avoid mistakes in writing?

I feel really unable to write alright. Can you give me some ideas how to improve my writing skills?

The only way to solve this trouble is, obviously, constant practice. You should repeat the rules of writing, practice them and analyze your writing. While learning, and in case you need, you may use different writing services like this one http://essayontime.com.au/the-top-assignment-writing-service-in-australia
to help you deal with your tasks They will certainly help you, or revise your works if needed. Meanwhile, do not waste your time and work at yourself.

You would need to practise much and read many good examples with it. Try to concentrate on your main mistakes and do not forget about it all. My recommendation is to go to "Prime Writing" service, ask them to proofread your work and see where your weak points are.