One of the most important parts to cooking is internal temperature. The main reason that's important is so you don't kill yourself or someone else with raw food. (kind of kidding, kind of not)
The best way to make sure you're not killing anyone, to make sure your meat is exactly where you want it (and to keep eye on your temp from the couch when it's 20 degrees outside) ... is to get a digital remote thermometer.
I have 2 Maverick remote thermometers and love both of them. The first one I picked up at Bed Bath and Beyond when I first started, and haven't had the first issue with.
My second thermometer is the ET-73, which comes with a meat probe and a temp probe. This is perfect to hang through the grate, so you can read the cooking temp near your meat too.
If you want to find these or more thermometers you can go to Bed Bath and Beyond or visit Amazon.com