Here’s a great tip from Rand Fishkin.

Find multiple pages on your website that rank for a single keyword and redirect the lower ranking ones to the higher ranking one. You can find those pages by Googling “keyword site:yourdomain.com”. You can then redirect the lower ranking pages for that keyword to the highest ranking one. Let’s perform an example.

Let’s say your keyword is “auto parts store”. If you have three pages ranked on Page 1 of Google for that phrase, let’s say in positions 3, 5, and 9, then you can redirect those pages at positions 5 and 9 to the the URL that is in position 3. You do this with a 301 redirect. The effect will be any traffic you get on those bottom two pages will then land on the top page instead. The end result will be a higher ranking for that position 3 URL. You could end up in position 1.

Another effect will be the PageRank from those pages that were at position 5 and 9 will be redirected to the other page as well, giving it more authority. And since that higher ranking page will get more traffic than it was getting before, that will result in more authority and higher search engine ranking. So you are likely to find yourself in a better position all around.