One of the Best RPGS of all time, the story is amazing and the world is hugeee!!
My recommendation for combat is a combination of the Quen sign and dodging (not rolling)
The Quen sign can withstand the first attack of any enemy with no damage, is basically the perfect shield, in theory if you have Quen activated you can withstand one level 100 attack with no damage, but only one so be careful with enemies that do combo attacks, so be sure to have Quen active before entering a battle. And you can also activate Quen during the battle so if the shield is down you can put it up again but be careful not all enemies will allow you to activate your shields again that easy.
Dodging is the best way to avoid damage without wasting any stamina, Rolling will allow you make some space between you an your opponent but it will drain a lot of stamina.
Oh and one last thing try to craft the oils for the monsters, the oils will make the different species of enemies more susceptible to damage.