Obfuscate
Some things work against some of the bosses, some don't. The best thing to use against some of the bosses, up to Ming Xao, is celerity, if you can get it, as well as blood buff. Against Ming Xao, you can also use the Spas-12, or whatever it's called. Save as much ammo for it as you can. Same thing for the big fish dude. It doesn't matter the clan you are, the Spas-12 is about the best for most, long distance, enemies.
"People should not be afraid of their governments, the government should be afraid of it's people." V from the movie V for Vendetta