Slayer for us plebs. Leaguestarter and Uber Lab farmer.

Try to get a 3Linked item asap and socket in Frostblades, Chance to Bleed and Onslaught.

Around lv 6 you get a reward from Tarkleigh, grab Ancestral Protector for more attack speed and some support damage.

Buy a Molten Strike for single target damage. Socket in Ruthless if you have a 4L with the right colours (Frostblades-Chance to Bleed-Onslaught-Ruthless.

Chose these Rewards from quests:
Tarkleigh: Ancestral Protector, Leap Slam
Nessa: Added Fire Damage

Put down Ancestral Protector in every fight for your attack speed to be less shit.

Buy Sunder. If it feels better than Frostblades, switch.

After the spider in act 2 has been defeated, get Blood Rage and start using it.

Buy these from Vendor:
Faster Attacks x3
Physical Projectile Damage
Melee Physical Damage x2
Elemental Damage to Attacks x2

Chose these Rewards from quests:
Greust: Herald of Ash

Good damage setup for Sunder
Sunder-Melee Physical-Elemental Damage with Attacks-Faster Attacks

Travel to the Mana leech-nodes asap, and grab all adjecant to Spirit Void
Tree at lv 30: https://imgur.com/a/FNBb2

Somewhere around here 4L will start dropping. Use essences and alchemy orbs on normal gear with links in the right colours with chances to get a lot better upgrades.
My axe, alc'ed and crafted attack speed https://imgur.com/a/PQiMZ

Chose these Rewards from quests:
* Piety: Cyclone
* Golem: Pick whatever golem you like. I chose Lightning for the slight attack speed boost.

Get Ancestral Warchief and Anger and level those. Also another herald and use it, if you have the mana.
I also used a random Vaal Skill, that dropped, for a couple of levels for faster clear and damage, Summon Skeletons.
Haste is also a good option for faster clear and smoother playstyle. It all depends on your mana reservation and the colours of your gear, there's not much use in spending chromatic orbs on changing the colours of your gear just yet.

After Piety is defeated, you finally get Multistrike from Dialla as a reward. If you haven't started using Sunder yet, now is a good time. Sunder-Multistrike-Onslaught-Faster Attacks.

But another Multistrike (to pair with Molten Strike) and a Greater Multiple Projectiles and level it in your secondary weapon slot or where there's room.

You can also get a Cast When Damage Taken and an Immortal Call and fit those in for better survivability.

By level 40 you may have reached the keystone Resolute Technique and grabbed several linked items to fit in all of your skill gems.

Lab Time!
Equip 3-4 life potions for precaution. The traps can be troublesome if you're not used to the layouts of the lab.

You can check https://www.poelab.com for layout (it changes once a day).
Try to get as many Darkshrines as possible for an easier labrun.
When the lab is finished, chose Slayer as ascendancy and you can now chose:
Bane of Legends: For speed
Endless Hunger: For better survival.

Chose whichever you feel like you need at this moment, next lab won't be much harder when you do it around 2000 life.

You can start using Cyclone and run through almost the entire game comfortably with a 5-Link.
Cyclone-Faster Attacks-Melee Phys-Added Fire-Elemental Damage (3R2G gem sockets)
I experienced it to be slower clear and worse than Sunder, but better survivability because we're dropping multistrike and we are also always moving.

When you've reached 4000 life, Merciless Labyrinth should be safe enough to ease through on your first try.