Your keywords are dropping? Have you been building link to your site? Are you just talking about on page seo? Have you made any changes to your page before they started to "drop"?

Be more specific. Don't expect people to evaluate your site when your are not even putting in the effort to provide more information.

Be sure you are including off-page SEO to your SEO plan. One-time changes and keywords within your site are fine, but won't get you the long-term SEO results you need to stay at the top!

Dropping sometime is a term of "google dance". You can get back to your position for that case.
But You can also dropping if google is not trusting your site anymore. Planned dropping can happen as well if someone have a better backlink rather than yours.

Just carry on building backlinks, it's all part of the 'google dance' as previously mentioned, you just need to carry on like normal, building stronger backlinks would probably help you get your rank back.

Thanks for your help. I have multiple problems.
1. My keywords are dropping.
2. There is variation in my site Google Cache Date. Yesterday Google Cache date was 21 FEB, today i checked again and it is showing 19 FEB. Why there is this type of variation. I am thinking, Cache Date should be new than 21 FEB.

I am doing off page optimization. I am giving my more time on forum discussion. I am getting links from forums. Is it right approach or i should move to blog commenting.
I hope you will understand my poor english. I look forward to you guys.

That's called the Google dance...its normal for sites to move up or down in the SERPS....hell tommorrow you could be 3 position higher than before....as you offer Google more backlinks to digest your site is going to move up or down so don't fret over it....could be your competition is doing more than you on promotion efforts..check them out as well..i always keep tabs on my competition to see what they are up to as well.