^- Agreed. The guard skill is one of the most important ones to get; if you time it right, you can order your partners to guard right before an enemy hits them with their special attack and it greatly decreases the damage.
I don't have the list of tamer skills to see what else is good for your playstyle, but IIRC I focused on increasing the partner's parameters after digivolving, learning enemy moves, HP & MP regeneration while walking and passing on the partner's stats. Basically, I wanted to get my digimon powered up as fast as possible while also ensuring the next generation gets a good head-start.
I ignored skills like cooking or gym training until the very end because I never used them much.
Kranky's FFXV picture blog: https://ffxv.crimsonkeep.com/blog/ "Bring on the boom-boom!!" ~ Sheldon J. Plankton