There's some great advice in here, I might be reposting some..

Use a mix of force, hold, and relax joints for starters in all modes.
Un-gripping a hand when you both have hand-grab can radically effect position.
If you're in a bad position reset with c and start over on turns, try to be unpredictable.
Allways go for landing over striking, if you're hitting the ground hard, relax certain joints to 'cushion' the impact.

If you're playing relax style, always keep a 'base' i.e knees, ankles - your movement should be subtle try to use opponents momentum against them, use relax to get into a good position then go solid for next turn to lock position.

I got better at judo dm, by loading up replays and making counters for starters I was having trouble with, also your own mp replays can show you a lot about cutting out mistakes/improving decap/dm/throws.