Ok here's what I've learned but it was learned in Canada, your wood might differ. I use the same wood for hearthboard and spindle, doesn't matter which ones but don't use conifers/softwood as it has resin that heats up and "polishes" that causes squeeking and chirping. Poplar is good, cedar is really good (although a softwood) but kind of cheating The top of the spindle should be as small as practical to reduce friction. So make it "pointy" and about 1/4" at the top and the bottom needs to be 3/4"-1" in diameter and a blunt point to increase friction, although it should usually wear itself into a blunt point anyway it's easier to start like that. If it's chattering and squeeking stop and use different wood as it's not "grinding" the wood and making punk. Using saliva or anything water based causes the wood fibers to swell and bind, better to use the side of your nose or run it through your hair to pick up some oil, the best lubricant is powdered graphite from a pencil. Another reason to put a pencil in your survival kit!
Here's the biggest tip you'll ever get about this stuff so pay attention to the bow! Dont' use a bent stick for a bow, use an "L"shaped stick with the handle being the smaller part of the "L" This allows you to leave the thong a little bit looser and is much easier to wrap around the spindle. Then you squeeze the thong under your little and ring finger and apply/release pressure as it suits you. This allows way easier spinning and stops the spindle from popping out because of too high a tension on the thong popping it out. It seems with a bow you need to start with too high a tension because it loosens up, usually just before everything comes together-a most inopportune time the "L" shape is magic indeed!
The bearing block is best made of stone if you can but not necessary and cheating a bit if you're interested in doing it for survival purposes. My take is if you have to bring a stone bearing block to make it work then just take a Bic lighter, but for learning purposes they do indeed work better. Reread what I said about graphite it's the best.
Make the spindle the length to bring it up to just below your knee when you're in position. Your hand that holds the bearing bloc must be held firmly against your shin so it doesn't wobble about. If you want you can make the spindle kind of octagonal instead of round and the thong really works better. Also making the spindle thinner in the middle than the ends will help the thong to ride in the middle of the spindle. Both of the last points are kind of "guilding the lilly" and not really necessary but nice.
Once you've got your equipment all set up, start slowly and make sure it all works well together. There is no rush!! Get it spinning nicely and spin away for a while, then stop, Stopping does some good stuff, gives you a break, and allows the wood to dry out a bit because of the heat you've generated, and you can take a look and make sure you're generating nice punk. The punk should ideally feel a little gritty. Maybe chip a bit off the bottom of your spindle before you start again to ensure you're working with virgin wood that hasn't gotten polished up. Then get it going again , slowly at first until it's smoking well then a few more seconds to really heat things up then squeeze the thong harder and really start to stroke it like you mean it and keep going until the smoke is pouring out.
Slowly lift out the spindle without knocking the fireboard and see if you have an ember. If you do take your time getting it into the tinder bundle because it's going to burn for quite awhile before it runs out of punk to fuel it.
So there's way more info than you requested but it's what works for me, maybe it'll help someone out.