Depends a lot on the niche and geographical target area as to what you can do about it. If your site is only for US customers for example then make sure your ads are set to only target the US and not to show for any other countries, even if your site is for a worldwide audience then it may be wise to set the ads to only show for countries that you think are likely to return a good ROI for your Adwords spend. Also make sure your ads are targeting very specific keywords, in Adwords its easy to go with the suggested keywords but in my experience this results in a lot of wastage as your ads are shown (and clicked) for keywords that are vaguely relevant or sometimes not relevant at all, personally I target specific keywords or phrases by wrapping then in quotes, doing this ensures my ads are shown only when the exact phrase is searched for by a customer, rather then a single word from my phrase which often isn't relevant on its own. Phil
When you say that you are getting junk leads through adwords, it simply means that your adword campaign has not been optimized properly. You have not been targeting right keywords to your right audience.
wrapping then in quotes, doing this ensures my ads are shown only when the exact phrase is searched for by a customer, rather then a single word from my phrase which often isn't relevant on its own. This isn't how to specify an exact match - square brackets is an exact match, you're choosing phrase match, which means your ad will be triggered for the keywords you specify, and in the order you specify but may have words before or after.