Once you reach High Rank, the armor skills and gem combinations you use become more and more important. Going into those harder fights with a mismatch of skills that don't build your character up in a meaningful way becomes a bigger and bigger handicap.
Of course it is all relative to the weapon type you have chosen to run with mainly, but offensive minded character builds(No Shields) want to generally rely heavily on skills like..
- Weakness Exploit
- Critical Eye/Critical Boost
- Attack Boost
- Health Boost
- Stun Resistance (Saves you from many needless cart rides)
If you are using Shield weapons, the type of skills you want to rely on are...
- Weakness Exploit (Will be the only DPS oriented skill you need, max it if possible)
- Guard up
- Health Boost
- Stun Resistance
Outside of that you can add situational things that suit your needs to those general foundations, things like Non-Elemental Boost, if using an elementless weapon, which I recommend. Flinch Free, if you are using faster, combo based weapons and don't want the interruptions during an important combo sequence. Earplugs, for the same reason, monsters roaring in the middle of important combo sequences can be a pain. Handicraft, if the weapon you are using is great in every way except it has crappy sharpness, remember upgraded sharpness colors increase damage, penetration/bounce, and critical chance with each higher tier. Slugger, if you are using blunt weapons that can already stun, this would increase your stun potential, stunned monsters are a great help for you and your team mates.
Hope you found this helpful