Any skill to boost overlimit like extended it, getting more gauge per kill, etc... Then just have some limit bottles, and depending on what you're doing, go wild. If you're farming grade, make sure you have minimum damage set and NPC's set to only defend and not attack. Depending on how many enemies pop on screen from linked encounters, you can basically cast with impunity with overlimit recharging constantly. (I recommend starting with at least level 4 ready, but only use 1 level at a time depending on what you're doing)

Check the guide here. It mentions the Tidal Wave thing and the skills to use in the middle.

https://gamefaqs.gamespot.com/xbox360/945075-tales-of-vesperia/faqs/54248

Thanks.