When conducting a usability test and finding people to take part: on the one hand some one is better than no one! but the ideal is to test on the site's target users. This involves thinking about who this site is for, a good way to do this is to use user profiles and personas.
We recently tested the Time Squared website using a one to one task based testing method. A week before the test we started looking for suitable participants. Finding target users can be challenging therefore the more time you leave to find them the better. For this test we used existing Time Squared customers and worked with a market Research agency to source segments of target users.
The results harvested a wealth of information which enabled us to sit down and discuss areas for site improvement. We are in process of implementing these changes as we speak. We will use Google Analytics to track how the changes have improved traffic, basket drop out rates etc.