You’re smart to ask about this. Over tightening lug nuts can cause damage to the studs to where they cannot be properly seated again and can even break them off.
IMHO Keith has given you excellent guidance. A “click stop” type torque wrench can be bought very inexpensively. Here’s one source. Click on the individual wrench to see its range. My lugs are specced at 78 ft-lbs, you’ll need to get your spec from your owner’s manual or, if you don’t have one, the dealer parts window guy. Ask nicely and he’ll be happy to look them up.
http://www.harborfreight.com/catalogsearch/result?q=torque+wrench
I keep a preset torque wrench in my trunk with a deep socket of the right size already installed, because flats always happen to me on dark rainy nights and I don’t want to try to find the right spec and set the wrench under those conditions. You don’t need anywhere near the accuracy you would if you were rebuilding an engine, so the calibration from the factory is fine.
Enjoy. And keep asking questions. The smartest people in any room are always the ones asking the questions. Bank on it. 