Basically, this varies from site to site and you have to experiment with different position to find out which one do the best in your case. Generally it may be on the top left (sometime right) corner.

In my experience in most sites a leaderboard adsense block below navigation menu gets the most clicks but you will never know for sure without trying and checking what is better for your site...

Google posted a heatmap on their help site indicating the positions that do well. (I'd post the link directly but don't have enough posts yet...just Google "AdSense heatmap" and you'll find it). I've found that those positions indicated do well.

Website header is the better place to optimize our ads performance. And the 300X250 size ads in the right or left side top of the page can get more clicks.

Try placing the ads in header or below the navigation bar. You can also include the ad beside the logo of your website in the header position. Rest of the places depend on the type of design your website has. If it is of magazine type, place it on the right side of posts (in side bar).

floating text links at the start of your post get's a lot of clicks on one of my sites, it outperforms every other ad running sitewide.

I agree with your website header or footer is very good position,but most effective between your text.Normally image ads got high chance than text ads..