Going back to the beginning, when I first started training there were a handful of ''fundamental'' rules I had to follow with regards to my training. One of these points stands out for me and I notice many people fail to do it, even experienced trainers. In fact, I will put my hand up and admit to sometimes forgetting it. I am talking about breathing properly.
Remember to breathe!
Many people will hold their breathe or breathe at the wrong time during their repetition. This is very simple so I won't drag it out, remember to breathe OUT as you press the weight and remeber to breathe IN during the negative part of the repetition.
This can make a considerable difference to your strength, endurance during the set and power. Nail this technique and your training will greatly benefit!