The spotter need to place his or her hands outside the lifter's hands and stand with a straight back, so they will be able to hold the weight in case that the lifter lose his strength in the middle of weight training. A spotter basically there to provide safety measures for those who want to challenge the next level in the weight training
Generally, what a spotter needs to do when assisting any heavy lift which involves possible injury would be to be highly aware of the situation and attentive to the amount of effort given by the lifter towards the lift itself. It the spoter sees that the lifter cannot push through to complet the rep completely, then the spotter steps in and tries lifting the weight off of the load partially.
