There are different styles but the one I advise and use personally is customized by John Hodgson which is originated from Dorian Yates methodology with a couple of changes.

Training is the stimulus/catalyst for growth and growth can only begin over a length of time if using the correct training technique with enough intensity & stimulation to the muscle fibers. If the muscles aren't constantly forced to adapt & grow with steadily heavier weights, overtime there will be no need for the muscles to grow as the stimulus has stayed the same. However, if the weights being used are slowly increased, the load on them will be heavier & therefore more fibres are recruited to cope with this extra weight, stimulating growth.

By training in such a manner the muscles are forced to adapt by becoming bigger and stronger, this is termed as Progressive overload.

The principles of H.I.T. is to put maximum effort and intensity into the final set after sufficient warm ups, where by you perform one set to failure and with the aid of a training partner perform 1 or 2 forced reps to finish off the set. This set is the message that tells the muscle to grow. The rep ranges i personally use alternate from week to week; 1 week is heavy week where the reps are lower (upper body 6-10, lower body 8-12) & higher rep week where upper body reps are 12-15 & lower body 15-20. Please note that even though it's "higher rep" week this still means going as heavy as possible using strict form & all out intensity on the final set.

A simple way of looking at it is this - The HIT principle of one all out set is like switching the light on. When you want to switch on a light, how many times do you have to flick the light switch to turn the light on?

ONCE!