Originally Posted by dutret

First off you need to understand what type of building up you need to do.

-Is this a 200m hill where you stall and simply lack the strength to make it past the crux?
In this case you have a strength issue. You should work with very very short intervals and complete rest between and possibly start going to the gym. What others have suggested an use ride longish hills or short ones over and over with no rest is wrong. You should also think long and hard about clipless. there are lot's of super steep short hills I lack the strength to make it up with clips and straps that aren't a problem at all with clipless since my back leg can pull much harder.

-Is this a slightly longer hill where your legs are burning and you're gasping for air until eventually just can't take it anymore?
Then you have a LT problem. Do medium length intervals with shorter rest times as suggested above.

Quite frankly just riding more will solve either problem if you aren't in great shape now... If that is the case gearing down at least temporarily is a very good idea to prevent hurting yourself.