Both knotting and braiding are one of those things that you have to "get the hang of" before things settle down. Once you get over the hump in the learning curve, you'll find that more and more complicated designs etc just need more patience and attention to detail, ot necessarily any new skills.
For friendship bracelets, I'd start with 6 or 8 strands, and just work the knots one direction. If you are using colours, you'll end up with diagonal stripes. The "trick" to getting the smooth surface and nice patterns is that you want the tail of the yarn you are working with to end up pointing the direction you are going - so if you are starting with the leftmost yarn, it needs to go _over_ the next one, then under and back through the loop - remember to do this twice for most patterns:
Oh, and make sure to secure the other end of the yarn bundle to something. Use a safety pin and fix it to your pant leg, or use a hook at desk level. I normally tie it around my big toe for simple braids. I saw somewhere that using a nail or hook in a short piece of board made it easier to keep track of the strands, and you can put pins or notches (like Willeke's cardboard maru dai) to keep everything even more tidy.
I'm thinking about starting a "Ben Scott" replica, and if I do, I'll fully document the process. It will be a pretty daunting set of instructions though. The best way to understand the more complicated slings is to practice little sections and work your way forward until you understand what is going on just by looking at the pictures. Trying to follow step-by-step is too much for a sling like this - the 20-30 hours that Barak and Ben talk about is for two guys who already know how to make these!
I've never done any friendship bracelet type knotting with anything other than simple stripes, so I started a little sample last night to get the hang of it. The pattern is really easy once you get going. The first couple of rows are tricky until things settle down. I made a simple split (and quit with the pattern) and then tried bringing the two side back together using Ben's hinge/pad technique.
Stick with it! I think the best first step would be to do the diagonal stripe bracelet for a few inches, then see if you can figure out one of the "V" patterns (they don't twist). Once you can do that one without too many mistakes, try to split and rejoin the sides a couple of times (do this from the "V" style, it makes more sense). My next step would be to but a FB pocket on simple braided cords, maybe 4x4 strands round, or 8x2.
Doing the fancy Andes-style braids is another problem! "250 Braids" is pretty good if your library has a copy.
Imagine the end result though. A sling to be proud of!
Matthias