Getting your weighting correct is the biggest thing you can do to make learning neutral bouyancy easier. If you don't have enough weight, you'll find yourself expending huge amounts of energy (and gas) kicking to stay under the surface (or stuggling to even get below it). On the other hand, a classic sign of overweighting leads to the following senario:
"I descended and added air to my BCD to get neutral, all of a sudden I started sailing toward the surface, so I dumped a bunch of air to drop back down. Once I got back to the depth I wanted, I added air to my BCD again and thought I was ok, till a few moments later I was once again floating towards the surface ... will this never end?"
While a diver with good bouyancy skills can dive with quite a bit of extra weight, here is why it makes learning bouyancy so difficult.
Suppose you have 8# of extra weight on you (beyond what you need) this means you have an extra gallon worth of air (1/6th of a cubic foot). As you decend that gallon sized bubble now gets reduced in size due to the pressure. When you arrive at 33 feet it is now half it's orignal size, meaning you must add two quarts of air (plus more to account for suit compression, but we'll ignore that for this example). You add the required two quarts of air, bringing you back to a one gallon bubble, making you neutral in the water. As you are swimming you continue breathing, but with every breath you take, you rise and fall. This means that if you inhale and rise 3 feet the one gallon bubble in your BCD expands by nearly 10%. As you exhale you won't go down quite as fast as expected due to this extra air in your BCD. On your next breath you rise a little more (now you have 20% extra air in your BCD) and you find yourself in a sudden unexpected ascent ride. In response you dump enough air to get a little negative, but as you decend the cycle starts all over again. By the end of the dive many new divers are considering giving up on Scuba.
"How do I figure out how much weight I really need" you may be asking. Here is the way I do this with my students.
1) Weight belt with pockets
2) As much weight as you normally use, but make sure much of it is in 2# blocks + a few extra pounds if you think you will be too light.
3) All your dive kit for the conditions you normally dive in (same wetsuit, tank, BCD etc..)
4) 5-10 feet of water. If you dive in salt water, do this off a calm beach, if you dive in fresh water a pool will work. (you can also add 3% of your total body+gear weight when going from fresh to salt water, but it's simpler to do it in the same conditions you dive in I think)
5) A good buddy (you weren't going alone were you?)
1) Drain your cylinder to 500 psi while near the bottom in 10 feet of water.
2) Empty ALL the air from your BCD - have your buddy make sure NO air is left in your BCD.
3) You should now be on the bottom, I recommend you lay down on your belly (might as well practice good trim/posture while you're doing this).
4) Clasp your hands and cross your ankles (avoid ALL finning/sculling)
5) Relax, and get into a normal breathing cycle. (be sure to check your SPG every once in awhile as you don't want to run out of air - if you are worried start with 700 psi - the goal is to finish the weight check with under 500 psi, while your tank is most bouyant)
6) Once you are relaxed signal your buddy and have them begin taking 2# of lead off. (this is where it helps to have a pocket style weight belt)
7) Continue removing 2# blocks of lead until you slowly rise off the bottom when you inhale, and sink when you exhale.
8) Go diving! (once you fill your tank that is)
You should now be correctly weighted. Now when you have a problem you know that weighting is not the cause. I may be due to air trapped in your BCD, sculling your hands or finning upwards (common on descents).