Well, for the range, you have to remember on thing, if your device is within 10' its possible the hiders was the same. so depending on the day, the cache could be in a 20' circle where you are looking. does that make sense?
Just like anything, caching is all about experience, if you haven't been out with a veteran cacher, try to find a local meetup and get to know a couple others in the area, they can help greatly with bringing your success rate up!
Most of all, don't get frustrated!
You will get it, have fun!
:idea: for those of you that are curious about what were are talking about, check out
http://www.geocaching.com
Geocaching, is a GPS powered, worldwide scavenger hunt. There are caches hidden everywhere, theres probably even a couple hidden along your favorite local bike path already!