Been seeing alot of little beaded snakes popping up lately so here's what I learned making a whole pile of them before I got one I was happy with. The biggest mistake I made early on was using too big a bead. Anything larger than 15/0 and the body looks chunky and the curves get stiff. Small beads are fiddly at first but after a day your fingers adjust and the taper acutally works.
Second thing: tension. You want it snug enough that the tube holds its shape, but if you cinch too hard the whole thing curls like a corkscrew and you can't flatten it back out. I keep a scrap of the same thread nearby and test the curve every inch or so. For the head, do the eyes before you close anything up. Trying to stitch two little black beads in after the fact is misery. Same with the tongue, do it last but plan for it, leave yourself a thread path coming out the front. Wax your thread too, at this scale it catches on itself constantly otherwise. If your first one comes out looking more like a lumpy worm, just keep going. My third attempt was the first one that actually looked like a snake.