This will come natuarlly, particularly on Extreme difficulty.
Any potion counts. Health is the obvious one to use.
The armour one is very helpful too.
Are the most useful, but you can experiment eith others.
Don't forget to make sure you're crafting health potions either in towns or on the road, as these are invaluable.
If you're trying to follow along with my Technical guide, these are immensly helpful.