Tips I can think of:
400 swim-- Dig your arms deep and close to your body. You get most of your power when your arms are at their deepest. Arms not too high when out of water (no gain there). Head out just enough to breath. No head "side to side" with each arm stroke. Don't kick too fast--you get 75% of your forward motion from your arms. These are tips my 2 competitive swimming brothers gave me in order to get my "3". But I was only able to do lap training once weekly due to my location.
The 400 IS a race!--You need enough points on these 5 tests to pass!
Tired Diver Tow--- Just push FAST. Yes, a straight line with no turns is best for speed. The more turns the slower your time will be. I assume you will not be able to CHOOSE where you'll do this....! IMHO, time allotments should vary according to where you have to do the test regarding turns. That's in a perfect world.
Equipment Exchange---This didn't used to be the 5th test, it was pass/fail. Ideally, get with a partner of similar size to yourself. Again, doubtful you get to choose. How one can get a grade as an individual when it's a team game escapes me, but that's the way it is now.
2 points. One is the obvious, that most people I've heard of do--start out wearing the other person's gear. This makes it much easier and is perfectly "legal" (don't let anyone tell you it's not). I did the drill twice (2nd time assisting in another DMC course). 1st time we aced it. 2nd time got through it OK, but we were way different in body size. How would I have been graded that time?
Other point is during buddy breathing- You or your buddy may be able to do considerably more than one thing after you take your 2 breaths. Maybe put your fins AND mask on, then get more air.
Oh, also, have a set plan beforehand of course. Well beforehand, as unless it's changed, the instructor can announce the tests on the spur of the moment.
Somewhere on Going Pro is the list of the (then) 4 skills and my own ideas on how to improve them to make them more practical for what you'll actually be doing as a DM. Not important to you now, but perhaps interesting.
Good luck with the whole thing!