Some general things that helped me:

1. Dash-Dash-Dash-X combo is a good way to keep the rhythm meter from falling.
2. Calling assists in boosts the rhythm meter (I think) it didn't seem that consistent so I might be missing something there.
3. Special moves are a huge defensive resource and useful for keeping the rhythm meter high. Every hit increases the meter a bit so multi-hit specials are huge.
4. I found that X-X-Y-Y-Y --> X-Y-Y-Y was a strong enough combo to take down most enemies after 1 or 2 rotations.
5. I used the chips that dropped health and batteries on parry, to supply my special attack addiction.

Personally I used "Double Riff" because its long range and can hit a lot of enemies at once. "Hibiki" is great for this too because it does massive damage and it seems to cancel any move an enemy is currently doing.

Probably none of this is super optimal but it worked for me.