I think my answer will be a bit different then the others here.
In my opinion, your first step should be to think about which feels closest to you - is it running around with a two handed sword? Maybe shielding your friends with your shield and be their guardian? How about a mage instead, blasting creatures away? A white mage / healer is always an option aswell. Not only could you heal yourself but also your friends and buff them too. Or maybe the bread and butter of fantasy games - an archer? When you decide which character is closest to you, then you can decide on what you want to do - while your immersion is intact and because of that you’re already enjoying the game.
Afterwards, when you decide on that you have to decide whether you want to be the killer, the healer, the defender or the supporter, but you already covered that yourself.
When that’s done, what you really need to look for is synergies. Having many strong skills will never outclass having many strong skills that complete one another. For example building an archer with a lot of dex and finishing it up with taking 2 ranks of rogue to have evasion effectively increasing your overall evasion by 50%. At that point in the game that 50% will be a rather big number, depending on your equipment. Or you can have a mage that drags enemies to the center of a skill and then having other aoe skills in that area aswell to damage all your enemies at once. Or a mage that links enemies together and increasing the damage at the same time. Or a warrior that increases his capability as he grows in ranks via buffs/secondary effects of skills. Basically you’re looking to empower your overall character every step of the way of building it. Or empower people around you and yourself.
Afterwards you have to read up a bit how gear works in this game. Gear, funnily enough, enables a couple of builds or strengthens others. A good example is viper bow that increases poison damage by quite a bit, making wugushi much stronger. There are many gear dependant builds out there. There’s quite a bit of very strong warrior builds too.
How do I come up with builds? Well, I’m practically never satisfied with the one I have so I’m reading up more and more, either debunking my ideas or strengthening my conviction that it actually might work. There is a limit to the knowledge however, not that much info on the game out just now, there are always unanswered questions. Don’t let it stop you from theorycrafting though, I love that part myself ^^
Hope it helps, though I might of gone off topic here and there. Here’s a mushroom for the fun of it 