1. Every color has a weakness:
Red is strong against Green, Weak against Blue.
Blue is strong against Red, Weak against Green.
Green is weak against Red, Strong against Blue.
Yellow is strong against Black.
Black is strong against Yellow.
Neither yellow nor black has a true weakness against red, blue, or green but all three can do damage against it. Keep this in mind if you find yourself stuck on a level that you can't be.
2. Level up/Rank up/Spend points wisely:
There are level ups in this game, Which earn you 1 point to spend towards HP, Attack, and Healing each time you level up. Never spend towards healing, Always put towards health or attack. Naturally if your character already has high health, Put it towards attack and vise versa. If the stats are even then put one point in each at a time, Switching back and forth each level up.
To rank up, You need to collect time fragments (earning certain ones on certain levels). Once you have enough, You can rank up. The max rank is 4. Ranking up means you can perform special attacks faster and more effectively. It's a must have if you wish to continue on with the game.
3. Combos Combos Combos:
The more combos you do, The more damage you do. So keep that in mind when playing the game because use of combos will be a huge game changer for you in the later levels.
4. Know what characters work:
I'd say a good 75% of the characters in this game are not worth using at all due to terrible stats so don't bother wasting resources on them. Instead put all your time and effort into testing your characters, see which ones work, and ranking/leveling up the crap out of them.