A basic framework for a leveling build to get you from level 1 to 70.
Corpse Explosion is your go to skill for killing mobs as your Skeletons will have no issues creating a couple corpses for you to get the explosion chain started.
The Passive Fueled by Death is still broken and not increasing your movement speed above the 25% cap, so adjust your build accordingly if you gain any items or group buffs that increase your movement speed.
If leveling solo, don't bother trying to get Leoric's Crown until level 30 when you unlock Blood Rush.
Always remember to:
Level up your Blacksmith
Craft a new 2-Handed Axe (with a socket) every time it's available
Always keep your highest level ruby in your helm and weapon for maximum XP gains and damage.
Grinding in the Fields of Misery and Halls of Agony is the fastest way to level, but only if you are regularly getting 400+ killing sprees. If you're having trouble maintaining those higher killing sprees, farm regular rifts instead.