I am promoting a site since three months but nor getting proper ranking. It comes in top 20 sites and then moves backward. Please tell me what should i do to make my site stable.
That's far too generic a question to get any useful answers from.
The best thing to do is to read the SEO FAQ at the top of this forum, which is full of useful tips and suggestions. Once you've done that, if you've got any specific questions, feel free to ask them in a new thread.
In the meantime, THREAD CLOSE.