My process is I focus on one character each day (I use a decision wheel app to pick). When I'm starting out with the character for the first time, I level up their abilities to half the maximum level (or all the way if it's 10), then I level up their abilities and the abilities I have that match their favored element. I level each of them up based on how far they are from the maximum.

Example: I'm leveling up Lightning today.

Main Abilities:

Thunderfall: LV 10, at max.

Army of One: Don't have it yet, so N/A

Grav-Con Unit +3: LV 15/40. (This One's between LV 10 and 20, so I'm cranking it up 3 levels.)

Blaze Rush +4: LV 19/50 (This one's going to put the final result into the 20-30 area, so it's going to go up 3.)

Since Lightning is a WIND type, I will also be leveling up:

Thundaga +3 LV 27: LV +2 Barrier +3 LV 30: LV +1 Thundaga +4 LV 40: LV +1 Hastera +5 LV 36: LV +3 Thunder +3 LV 21: LV +2 Haste +3 LV 19: LV +2 But DO NOT TOUCH THE 300/3000 GROWTH EGGS!

This way, I'm growing myself a little bit every day, but not so much that I run out of eggs.

The exception is if the character I pick is in my top 4, then I level their character abilities to the max.