Time in the water is what you need.
All this talk about weight and trim and strap placements and fins is all fine. But even when not properly weighted or trimmed out, an experienced diver can still hover motionless.
With more dives the weight issues will be corrected, but it's time in the water that matters the most.
When I started diving twin steel 130s, I could not keep my face out of the mud. As soon as I relaxed, my head dropped like a rock. I tried all kinds of gear solutions to fix a skill problem, but nothing really worked. So I just kept diving with twin 130s with my normal kit.
One day, halfway through a dive, I was totally relaxed and realized that I was not having any trim issues anymore. Problem solved with more time in the water.
Dive more.