When tightening a bolt or nut, use an ordinary wrench or socket to tighten the fastener down to where it is snug but not over tight. The final torque is then achieved by using a Torque Wrench.
A torque wrench must be used correctly to achieve an accurate torque reading/value. Hold the wrench on the hand grip, and either push or pull on that part of the handle only. Where the hand grip has a pivot point, you will have to hold the handle so the load is balanced over the pivot point.
If your application requires the use of an extension bar, then you must ensure the extension is kept straight and parallel to the fastener you are tightening. Using an extension won't alter the reading if performed carefully.
When using a torque wrench that is not a Torque Handle style Torque Wrench and you are using a crows foot open end fitting, position the crows foot so it is 90° to the wrench handle. This will assist in the accuracy of your torque wrench in that you are minimising any change in leverage. Be aware that if you extend the length of the wrench to slightly increase leverage by positioning the crows foot so it is straight with the wrench handle, this in turn, will increase the actual amount of torque applied to the fastener over what your wrench indicates. The difference between the torque wrench setting and the actual torque applied will be greatly increased. Refer to Precautions for Torque Wrenches with Extension Tools.