Take the mullein, and break them into little pieces and then go find some Teasel! (sorry, just my biases showing

)
Make sure you clean up the stalks well, or it will chew the hell out of your hands. I like to use a piece that is about head high when I'm kneeling down.
Start with your hands in a bit of a 'V' shape and a bit more open at your fingers than at the base of your palm (this is much more difficult to describe that to actually do

).
The part of your hands that contacts the drill should be the bottom of your palms. A picture (the blackened area is the part that contacts the drill):
This is the part of the hand that will blister, break, bleed, and eventually callus up.
As you're working down the drill, concentrate on moving both hands, rather than moving one hand, while the other is stationery. When you get to the bottom, hold the drill with one hand (so that it doesn't pop out of the board) and quickly move the other hand back to the top. Then move the second hand up to the top.
Usually when I start back at the top, I speed up for the first couple of twists (?) to bring the temperature back up.
Make the depression in the hearth a bit larger than your drill end. Burn in the depression so that you can see where the drill is riding, and then cut your notch. The notch does not need to go as deep into the depression as with bow drill, at least with Teasel because it's just the outer edge that creates the friction.
Also, relax your shoulders, the way you do a reverse punch, otherwise the muscle strain will cause premature fatigue (where's the laughing smilie

)
I'd recommend that you do not try for the coal the first few times, although you may get it anyway. Just work the drill, letting the muscles tune up for this movement. Also, let the hands toughen up. Of course, you probably won't do this, but that's what I recommend.
Or take the short drive up here and I'll show you first hand!
Doc
ETA, as far as hearths, Basswood, Poplar, Willow, etc. Pretty well the same hearths as for bow drill. I'll see if I can find my drill/hearth combos.
The drills may be dry enough, as is, once you trim the bottom off. BTW, Teasel (Dipsacus sylvestris) stalks can be straightened somewhat, using heat, like arrow shafts.
An older
thread you might like to check out.