Currently lvl 87 on Hardcore essence.
Leveled up from 9 to 70 botting with my Gladiator (87, 1h+shield) and my Champion (72, bow). First thing you need is good gear, some nice leveling uniques with life and resistence, and a good weapon. Without that, you can do nothing, because you MUST simply crush all mobs. Having 4 links for your single target and for your AoE spells is almost mandatory.
Then you need a good build, focus on defensive nodes (early game your gear damage will be enough).
Another thing i did, was to be overleveled.. I didn't just hit Quest Bot and Go. When i get to certain areas (Ledge, Chamber of Sins, Docks, Aqueduct), i keep the bot grinding there so i get like 5 more levels than the required to kill bosses, so things go very smooth.
It's all about getting prepared and know your stuff (the game).