Dual wield daggers or swords on your first weapon bar, and a bow and arrow in your second. Wear medium armor, and your potion should be a good stamina one that also has some health buffs. You need to want to be a vampire. The vampire ultimate should accompany your dual wielding, and you should use this to tank whenever your health drops when you are recharging your potions and/or just don't want to use your potion just for your health (if it's expensive.) Eat your food before you enter a fight, of course, as well, use the best one you can for stamina with some health buffs.

Hit em with the bow ultimate first when you enter a fight, while that is recharging (and your other one as needed) run around out of range of short-attacks and dodge long range ones while you use your bow and DPS. Swap to your dual wielding to pick off the little minions that come after you, and in close-quarters, and when bosses are temporarily disabled. You will do evasive maneuvers instead of tanking mostly, and tank when you are in vamp lord form which is premeditated by you almost dying and needing the instant health regen.

You should be attack weaving, and going through your abilities bar as such. I will be updating this with the abilities I have picked out, but most importantly you need to have a siphoning one which you can spam when you're low on health. This is not good to have when purely DPSing on a team, but you will die without it while solo-questing. This replaces your need in a team of a healer while you are out soloing.

Do a double bow build, with the bow ult and another power ult (I'll be updating w mine soon I wanted to get this draft out now) and basically your entire ability bars should be the most powerful attacks available to you. Your weapons should be the ones with the most attack damage, and your food/potions should only primarily buff your damage dealt. Absolutely nothing should be dedicated to health regen or defense aside from your armor being armor. That is your healer and tanks job to deal with besides you running around trying to dodge the obvious.

This is the trickiest build to do. You won't be attacking predictable and linear enemies, you will be going against another sentient mind. You will not know their playstyle or what they will hit you with. You need to be defended against the unknown, ready to deal some damage, and able to come back from some hits. And you need to stay agile, and move around or else you're going to be overpowered. Similar to your soloing build, dual wield blades on your front bar and swap to a bow and arrow set. You should lean on the night-blade non-combative support abilities as much as your pure DPS skills, and still have your vampire lord form ult to lean on to save yourself when you reach near-death and your potion is recharging. Always make sure you have your ult saved when you are getting beat, to make sure you can use it before it's too late if it gets to that point.