HiI know this will have been asked before, but should the descent be head up or head down?
Ideally you would want to descend in a horizontal position so that you can see what you are dropping on (usually some poor diver minding his own business )and also keep your fins out of the way of the silt, so you don't ruin the viz before you get to the bottom!
In a horizontal position you are also able to be closer to your buddy when travelling down a shotline for example. It is generally easier to descend this way and you might even use less gas, as there is no real need to keep moving your fins.
Many people will descend in a heads up vertical position, simply because they find it hard to stay horizontal and stationary in the water column, and that will make it hard to stay with your buddy (not to mention of course that they are simply copying their instructors, who also can't do this).
It takes a little time to learn but pays massive dividends in terms of comfort and control later, and is something I would recommend to every diver.
PS Unless you are on a scooter, then it is heads down as vertical as you can in full pitch dive bomber mode!