The engine needs to run under load or real world conditions to read them. You cannot do it sitting in the driveway. Depending on how much you drive it, you could need to check em after a week. If it's a drag only car, then do it at the track after a couple runs.
If you are fine-tuning to the point where you are reading the spark plugs, it can only be done accurately by installing a fresh set after the engine has already been warmed up. The best way to go about doing this is to warm the engine first, and then change to a clean set of plugs. After you have changed the plugs, go out and run a pass or two. You want to make sure that you shut the engine off clean—meaning shut if off on the back road after you run and don't let her idle too long. Once you have done that, pull the plugs and read them.
To properly read you will need a something w/light and magnification. I have a Dr's otoscope I use... benefit of being a biomed This is the one I have: http://cgi.ebay.com/Welch-Allyn-opt...8QQihZ002QQcategoryZ31472QQrdZ1QQcmdZViewItem
It works great. Places like Walgreens sells one of lesser quality, but it will get the job done.