Use the lloyds talisman, keep a close distance and make sure to rush if you see the start of the estus animation then punish them with a backstab. So keep a knife of sorts on you if you plan on doing a lot of damage to the chugging host.
If it's a 1v1 situation just parry/BS them and then throw a loyds on their corpse. Most usually don't have enough speed to roll away from that.
Can't give you much advise on ganks though. Never been great at dealing with them.