Some info:
If you are a Caster Int determines your damage.
Int adds not only to your skill it adds to your max skill.
Dex determines your damage if you are a rogue.
Str determines your damage if you are a figther.
Int determines your damage if you are a mage.
The higher your Dex the more often you will do your max damage.
for example 90 Dex: 10, 8, 10, 9, 9 20 Dex 3, 8, 2, 10, 2.
Your to-hit is determined mainly by your skill. Including mages, Your skill level with spells will also determine how often that spell hits.
Int lowers the cost of training. you will notice skills tend to spike at a much slower rate.
Con gets you HP and Stam. Stamina is the lifeblood of PVP. No stam you die!
Stamina is also the fighting classes Mana. No stam no special attacks.
My suggestion. Find your main damage stat and max it. Then you will have a secondary stat that controls your mana/stam max that as well. if Con is not your secondary stat I suggest in early levels split between Con and your other stat.
In the first ten levels, if INT is not your main stat get it up to at least 50. This will help later on during training. Then get your main stat and CON up. Between 10 and 20, focus on our main two stats and reserve two levels for CON. Then it is really up to you how you want to progress, you can then try and max main stat or split between main and secondary(Spi for casting professions, Con for melee professions).
If you are a pure mage DEX is useless to you!