Hi misterlizard,
I think the best way to improve dynamics, is to do dynamics !
Doing laps underwater, ie less then max distance is a good idea to get your muscles used to lactic build up, CO2 tolerance etc. Specially if you are new to it, try 10 or 20 laps(don't have to be full ones) is a good workout.
I found I improved most by doing at least 1 maximum dynamic each training session. Yes you need a buddy for this. I warm up by doing negative breatholds, you can also use a normal static routine like Deep thought suggested.
For me it works best if I haven't done any laps before hand, you do get a pretty bad lactic burn from it though. Then after this or on a different night do more repetitive laps, less then your maximum.
I had no idea what distances I was able to do until I started trying for a big one at least every week. Earlier in the year I finally made a 100m. Did it a couple of times then thought I'd turn around and swim a bit... did 117m, then 125, 130, and my best was 144m.
I wouldn't have guessed I could make that distance. But you can only do this with a trained buddy, who must follow along side you
towards the end of your dynamic.
Dive Safe !
Wal