Thats my first guide, i hope its understandable. I know my english is not the best im from Austria sorry for that. I still hope it will help you.
Make sure you play on Death March difficulty otherwise the enemies die too quickly. To apply bleeding its best to use broadhead bolts, they got a 100% chance for bleeding. Devils Puffball bomb for poisoning and the Dancing Star bomb for burning. I did the achievement at the Banditcamp Devils Pit since there are many bandits and you have a safe spot. Just lure the enemies to you and go outside the first gate. They wont follow you, and line up but wont lose aggro so you got free fire. Broadhead bolts can be purchased from most Blacksmiths and the bomb formulars can be purchased from the herbalists hut in novigrad