can you help me to understand that in on page optimization while choosing keyword if i have too keyword one having Hugh number of search result and other having very small number of search result in google adword then which one to use?
If your site is new one and content is also poor. Then in my suggestion you should go with keyword which having small no. of search volume. Select the keyword in such a manner that after ranking that keyword you can edit (means possible to make short keyword). So, you can easily rank the site for high search volume keyword.
It depends on your interest on the niche. Once deciding the topic or subject, just use google adwords keyword tool to get keyword suggestions and competition analysis for the suggested keywords and phrases.