Get a torque wrench of the appropriate range (in/lbs, ft/lbs, etc), set it to the desired amount and tighten the screw/s. The wrench will let you know when you've reached the setting--it will click, release, illuminate or such. Specific tightening techniques can be required for certain applications such as engine head bolts, wheels, etc.--bolts may be required to be tightened in a certain order/pattern/amount, multiple passes, etc.