I see the 3 biggest beginner challenges as learning to control breathing,balance and situation-awareness.
Breathing: Establishing a good breathing pattern before initial descent, focusing on slowing it down further, knowing that neutral buoyancy using the BCD is done after establishing good breathing.
Balance: learning to control the hips to go from an upright position (initial descent, venting BCD on ascent) to a horizontally trimmed position without kicking. Having the abdominal muscles slightly contracted to keep the legs from sinking.
Situation awareness: is knowing where you are, how much air you have, approximately how long that will last you at a given depth, no-deco time- basically respecting the rules of diving without having to narrow your focus on any one of them.
Breathing: Establishing a good breathing pattern before initial descent, focusing on slowing it down further, knowing that neutral buoyancy using the BCD is done after establishing good breathing.
Balance: learning to control the hips to go from an upright position (initial descent, venting BCD on ascent) to a horizontally trimmed position without kicking. Having the abdominal muscles slightly contracted to keep the legs from sinking.
Situation awareness: is knowing where you are, how much air you have, approximately how long that will last you at a given depth, no-deco time- basically respecting the rules of diving without having to narrow your focus on any one of them.