when you say related ads do you mean ads about a mobile phone on a mobile phone blog or are you selling ad space and want to find advertisiers? is your blog with blogger or wordpress etc?
First you have to check if there are ads related to your content. After that you should use the keywords in a way they can be crawled by the adsense bot and gave you related ads.
Posted the answer here: http://forums.digitalpoint.com/showthread.php?t=342808 Hope this is what you were looking for, MONEYSAVER.
Yeah, just get some quality content, and make sure the keywords are in your content. I don't know this for sure, but it might help to make the keywords bold..
make sure you put your keywords or any related words on your site metatags and contents. If you dont have any keywords on your site, google can not know what is your site content and it will give you a random ads. tell them what you are and they will give you what you want.
i have some suggests for you * use related meta tags with your content * block unrelated ads from your adsense panel * if you have images , using related file names and related alt tags in images
meta keywords can help a lot with this. Also using the keywords you want to target in titles. May take a little while for the ads to calm down so make one change and then watch for a few hours before you make another change. hth