1) Go to your Adsense account, click "My Ads", select "Search" on the left, click on "Custom Search Engine" and click "New Custom Search Engine".
2) Fill in your name, keywords and all other data.
3) In the "What to Search", select "blog friends" and write the full URL (including HTTP: //) of the site you want to search. You can simply add your site to show results from blogs / sites.
5) Now log into the blog dashboard and create a new blog page. This page will be the place where the search results are displayed. Better make the page name to "Search" and do not forget to not use an index tag for that page. So let's assume the name of your page is domain.com/search
6) So in the above image, in the URL field, you will add http://domain.com/search. Renaming a domain with your actual domain name.
7) Click the "Save and get code". You will get two codes. Listing 1 is to display the search box, and the second is to be added on the page where you will want to show search results that is, the page you created in step 5.
8) Go to the blog Dashboard and open your HTML editor from the page that you created in step 5. Place the 2 Adsense you had in the previous step.
9) Create a text widget and paste the 1st Adsense code.
10) All is well! You are done, Start earning from Search results.
[*] If your search box is looking big, find “size=” in the 1st Adsense code and set its value to a lesser amount.
Many Adsense publishers claimed that search box helps them to generate a good revenue. You can always configure ad placement for search while setting the ad or edit the already created channel from dashboard.