using these words

I never have to think about picking the right word, because the language defines the way I think.

What I am trying to say is, if I have something I wish to say, I do not need to worry about picking a word because I could not understand what I was thinking without having already known the right word for it.

Sometimes, I will know the word...but have trouble remembering it...and that can be quite frustrating and lead to writer's block.

The best thing to do if you cannot think of the right word to use is simply to describe what you are thinking by using other words...and then go back and change it later IF you still feel you need to later.

You should not let choosing the words slow down your writing...with writing, you need to get into the flow to produce good work...and if you keep disrupting that flow by stopping to think of words, you won't write as quickly or as well.

won't using new words giving me the chance to improve.In spoken English, we use almost the same words everyday , and I can't really give new expressions or words.Otherwise people will see me as a " geek"

But, your are right about bein yourself.

As stuh says, just write. Use the words you would use in speaking, and just get your thoughts on paper. Then go back, perhaps after a short break, and think about how the sentences are worded. If you can make improvements, do so. If your original writing clearly expresses your meaning, leave it as you wrote it.

You will gradually improve and learn, and have to correct less.

In the meantime, learning new vocabulary and practicing in its use will help you to write more fluently, but don't force the use of new words just for the sake of using them.

And please, keep asking questions about word usage. The dictionary can give you meanings, but English has many shades of meaning and nuances! Asking is a good way to learn how native speakers use the language.