There are a lot of secrets about creating good bleeders. But here are the basics.

Slayers have the best bleed
Theatrics have the 2nd best bleed

Snivlers give a bonus to bleed

Exotic weapons give a bonus to bleed

Slayer skill "Blood Bath" at lvl 10 usually inflicts between 200-400 bleed in a single hit.
Theatrics skills "Gratuitous Violence" and "Bloody Spectacle" improve bleeding rate.

Certain fighting styles improve bleeding rate...
Certain activity and blood lust improve or reduce bleeding rate too...

There is also "extra bleeding" rank on legendary items. Nobody I know has pushed the limits on this yet to see how much it can improve bleed rate.

Once I had a team in Conquests put 2700 bleed per round on Gut Thrasher