My general strategy for fights is to sloooow down and work more methodically. With most other 3rd person open world games, you can get in and out of a fight in less than a minute. With this one, I die and die and die if I try to move too quickly. Holding down the guard, parrying a bit, and taking my time to work a large group (or the griffon, just be patient and wait for the open shots) seems to be much more productive in the early phases.
I also started hypnotizing human enemies with Axii and then decapitating them with the strong attack. Seemed to work well. It takes an extra second to cast, so you need a little distance from the opponent.
Some other tricks:
using the d-pad left and right to change signs in combat
using axii on Roach to calm him down when horseback fighting
holding attack to slow time on Roach
selling your crap to the appropriate vendor for a better value