Hit chance cap: 7.5% (required).
Expertise cap: 7.5% (required).
Pet: a wolf. It doesn’t really matter because you will get all the buffs from other players. Be sure that your pet has the ferocity spec.
Stat priority for Marksman spec: Agility > Crit chance > Haste > Mastery. Haste is better than Mastery because you will cast Aimed Shots faster.
Gems: red = 160 agility / blue = 80 agility and 160 hit / yellow = 80 agility and 160 crit.
Abilities priority (rotation): Rapid Fire > Serpent Sting > Chimera Shot > 2 x Steady Shot > Aimed Shot > Aimed Shot > Glaive Toss.
The idea is to use Aimed Shot as much as possible when you have the speed buff from Rapid Fire and the double Steady Shots.