I have started many, many bow drill fires. (Although I live in NYC, I worked for survival schools throughout my undergrad).
1. Socket Rock: Use a low friction socket rock--sandstone is a no. If you really plan to rely on a bow-drill, it's worth to go rock hunting in advance of your trip for a nice palm sized, dense rock, with a right sized indentation for the spindle. I used a quartzite that became smooth as glass with use.
2. Spindle wood: Best spindles are standard american sage--artemisia tridenta. Other types of sage will not work as well or not at all. The next best wood is cottonwood. Since I spent most of my time in Utah I don't have experience with other woods. I have also used yucca spindles, but it is too soft for any real success.
3. Spindle shape: I like a spindle shaped like a big pencil, with a worn out eraser. The pencil end goes into the socket rock, the relatively flat rounded end goes onto the fireboard. I prefer about 3/4 inch to 1 inch diameter. For lenth, I like between 10 to 14 inches--shorter becomes difficult to manage because you're hunched over.
4. Fireboard: Again sage, around 1/2 inch thick top to bottom.
5. Bow: Key here is long and moderately stiff. I often used a sandbar willow around an inch thick. Wild tamarack is also good for this purpose. I thick you'd want at least 30 inches of string, so you get a good long spin each way.
6. String: I always just used regular, old fashioned packcord. Never tried leather. It would blow out after a while.
7. Tinder bundle: This is one of the keys to success. The best material is sage bark off of a dead sagebrush. The second best is juniper bark. The third best is the interior cottonwood bark. Select a nice legnth of bark. You don't need too much, maybe 12 inches. Hold in your hands, perpendicular to your fingers and then gentle breack in down a bit to loosen the fibers. As you do this, a lot of "dust" will fall over. Once you've loosened it up, wrap the bark around your thumb and tie it into a loose knot. Scape all the "dust" together into a pile and use your knife blade to dump it into your tinder bundle. Push it lightly inside the tinder bundle.
--Use to knife to create a score mark near the edge of your fire board, positioned so that the perimeter of circle burned by the spindle will just touch the edge of the board.
--Burn a hole by spinning the the spindle with long steady back and forth strokes. Press softly at first till you get a rhythm, and gradually adust your pressure and speed till you start to see smoke. Let it smoke a 5 or 10 seconds. The hole should a flat black and relatively shallow.
--when spinning the drill, hold the bow where the string is tied. That way, if the string loosens while drilling you can take in some of the slack with your thumb without starting over.
--Carve a v-shaped notch into the center of your burned hole. Don't be shy about it. This is a ESSENTIAL. If you don't do this, you will have a very difficult time starting a fire.
--Use the same technique again, long steady back and forth strokes. Increase pressure and/or speed if you're not getting smoke.
--The notch will fill up with brown and then black "punk". Keep drilling till the punk itself is smoking. The smoking in the punk means you have a coal.
--Carefully transfer the coal and as much of the punk as possible into the tinder bundle.
9. Blowing the fire.
--don't smash your coal with the tinder bundle.
--Blow gently till you see the coal glow red. It will grow as it consumes the punk. Then gradually compress the tinder bunder till the frayed strands of tinder connect with the tinder and keep blowing steadily.
--sometimes, you can get a flame just by waving the tinder bundle in the air--that seems to get real good air flow into the tinder and coal.