If you are pretty confident there are fish near a good piece of structure and you have dragged it in front of them and still haven't had a bite, dont give it more than fifteen minutes before you tie on something else.
If you are searching for fish, tie on a spinnerbait or a suspending crankbait and vary your retrieve speeds and depths to find fish. Be more patient here.
Still nothing, find new structure.
Try reading this too...
http://www.bassresource.com/fish/faq.html#news_6
Click on the link titled "How do I catch bass from the bank?".