Spider identification can be very tricky especially once you get below the level of the family classification. Species and genus-level determinations generally require a good stereomicroscope plus some experience. You can, however, usually figure out higher level classification by comparing your specimen to a drawing or photograph.
What's important for most people is to be able to identify the poisonous or venomous species, if any, where you live. In the US three species are commonly blamed for venomous bites: the hobo spider, the brown recluse spider and the black widow spider.
Once you learn to recognize and avoid the few venomous species you can relax. For all other spiders you should use a field guide with good color pictures and range maps to do your identification (see below).
is an in depth and specific guide to spider identification and a good place to start. Here's also an excellent collection of 
