When i am speaking in english , i use to make grammatic mistakes. how to avoid it?
This is one of the big problems with some "communicative" learning settings. It's important to communicate and to speak fluently, but it is also important to speak (and write) accurately. Some courses wait too long to start correcting grammar mistakes which may end up in fatal permanent errors. Sometimes remedial work comes a little bit late.

The only thing you can do is reading manuals on grammar that match your level. There are some good self-study guides out there. Register in a conversation club led by native speakers or good non-native models so that proper feedback is received. You have to work hard to overcome the errors stuck in your mind that come out unconciously.

Hope this helps! Emotion: smile
Thank you!