I think your English overall is quite qood. You obviously have a good grasp of it already.
Can I ask one thing though? Why the rush to learn? It will take time to increase your vocabulary, and the best way to do that is by practising writing, reading and speaking on a regular basis.
You could take a look at an article CitySpeak wrote for our website which might help you out a bit...
Taking Control of English - Tips on how you can speak and communicate better in English.
If you want any help at all, just ask us all here and we'll be pleased to help you.