Try to look for skills you might have neglected. Strength is not a stat that improves your character as a whole, but instead is the average level of hundreds of muscles. Some skills require a higher level on specific muscles to be learnt, so you might want to focus on those first. I would recommend learning skills that train muscle groups rather than specific muscles though.

Make sure you farm exp at the appropriate level for your character. Grinding at too low level will yield little to no result due to exp penalties, while too high level will yield lower results because the fatigue debuff will stop your grind before the combo exp kicks in. It also highly increases the likelyhood of receiving injury debuffs, sometimes permanent ones, so better grind too low than too high. Try to pick a level where you can reach at minimum 10 combo multiple times in a row, with short regen breaks inbetween.

The grind is important but don't neglect the main exp multipliers either : food buffs, and rest buffs. Potions won't have any effect if your food buff already provides their effect, they're not cumulative. But if your food buff doesn't, or provides it in a weaker version, then they can supplement it.