My question is - M doing work off page & on page both, fisrt month m doing complete on page like meta tag,headder tag, Google webmaster/Analytics etc… after completion of on page google crawl my website then the ranking is good. Then m doing 2nd Month start off page activities the ranking is go down. So what is the problem in my work.
It could be that you are simply suffering from the “new site” effect. Google sometimes - not always - give a disproportionally high ranking to sites that are new, simply because their content is fresh. As time goes by, the ranking settles down to a more “natural” level. This is probably what you are seeing, and is perfectly normal.
If you want to try to regain your former high ranking, concentrate on developing useful, fresh content for your site. And don’t worry about month-by-month changes in ranking.
The reason of this decrease could be several. I think you should not worry for now, just keep on doing off-page optimization as per Google guidelines, you will see some results soon.
For on-page, make sure that you have optimized the website pages completely like uploading content on page, using head tag, optimizing images on the site, posting blog, etc.
In which language are you trying to rank the site? No offense, but your English is not great, and that would probably hurt your ability to rank for English keywords.
In terms of offsite SEO, you are much more likely to hurt your site than to help it through link building. You may be best off by just providing content that your users will want to learn about and enticing them to share it with their friends who would also be interested.
You can’t judge the reason so early. There can be so many reasons for this. Just go on doing off- page techniques for some time and after that check for ranking.