I just got into act IV and it was extremely easy. For me personally, it is getting to be progressively easier, which i find a bit disappointing.
CORE skill. TRANSCENDENCE. To put it bluntly this skill makes you pretty much invincible because any spirit consuming ability will heal you for a decent amount. Furthermore, your mantra does not have a cool-down, so a heal is always available (i very rarely find myself out of spirit).
Fists of Thunder (Thunderclap) - Mobility is a must, as you will often find yourself in need of getting out of fire or poison quickly. In my opinion dash is not worth it, and Fists of Thunder is a very potent single target damage skill and one of the most potent spirit generators.
Deadly Reach (Piercing Trident) - A very potent AOE damager that generates spirit? What more can you ask for?
Serenity (Reap What is Sown) - 'Oh !@#$' button #1. If you are out of spirit and in trouble, pop this one and start spamming Fists of thunder (single target) or deadly reach (multiple targets)
Seven-Sided strike (Several-Sided Strike) - Extreme AOE damage plus decent heals due to Transcendence. I rarely find a need to use it, but when i pop it - everything ends up dead (including champs).
Breath of Heaven (Circle of Scorn) - 'Oh %^-*' button #2. If spirit is high and health is low.. it's the one to use.
Mantra of Evasion (Hard Target) - Believe it or not i use this one as a heal very often (no cool down). In addition it makes sense to use it before the mantra effect ends due to a 3 second 15% dodge chance.
Resolve - makes things easier.
The guardian path - makes things easier.
You need to stack the following:
Dexterity (auctions are overflowing with these items and you can specify 50+ Dexterity requirement in your queries); Cheap and effective.
+ Damage jewels (OP) and + Damage items; If you have a weapon with a socket and your jeweler is level 4 or up, you can double your DPS. SICK!
+ Attack speed; Will significantly improve your DPS.
Vitality (you do need some)
Pick fast weapons and dual wield, with your defensive abilities and non-stop heals you do need a shield.