Archer
Here, your main damage will be Multi-Shot, then spam Oblique Shot when MS is on CD. Full Draw has a “Pierce” property, so use on skill rotation.
Swift step is optional, since it’s only good on Archer C2 (+25% critical rate attribute), if you want, you can dump 5 points on the 3 damaging skills and don’t have Swift Step at all.
Falls off at Ranger C3
Ranger
Main damage skill here is Barrage (before C3) and Bounce Shot for multi-target, Critical Shot and Spiral Arrow for single target. High Anchoring is for “sniping” enemies on a straight line. I don’t know how Steady Aim will work on iTOS, but you must activate it before using damage skills.
Falls of at Rank 7, but still useful
Fletcher
Here, use Crossfire and Magic Arrow for multi-target and Bodkin Point and Barbed Arrow for single target. Don’t pick the burn attribute for Crossfire, because you will gain CD on a 0s CD skill.
Cannoneer
You will love Cannon Blast and Siege burst 
For a good PvE stat, I would recommend:
2 STR, 1 CON, 1 SPR, 3 DEX
STR -> more physical damage and critical damage, plus you gain a 10% STR each rank up
CON -> more HP, you will need on higher levels
SPR -> more SP and block penetration, some mobs have an annoying block rate, so it will come in hand
DEX -> Self explanatory, more critical rate, accuracy (though you won’t need on PvE) and evasion