I was probably into the 3rd or 4th week before I figured out how to do it. For the first few weeks we had him in a co-sleeper thingy between us in bed, and it sucked because my back hurt really bad sitting up in bed (plus I needed to sit on one of those doughnut cushions due to a giant healing perineal tear), so every time he was hungry I'd have to lift him out of his bed, get up and go over to a chair and get all propped up on my pillows- then he'd fall asleep nursing and then wake when I tried to put him back down...and then I'd end up going downstairs with him so as not to wake DH while he was fussing...and then he'd fall asleep in my lap again only to wake AGAIN when I tried to put him back in bed...and on & on.
DH kept telling me to "just nurse him lying down, that's what you're supposed to do!" and I was like HOW??! I would try and it just seemed so awkward! We have no LLL chapter here, and having people describe it to me on the phone was no help. I think it was in one of Ina May Gaskin's books where I finally saw a picture and description that helped. At first I had to prop up on my elbow a little while he latched on, and then slide down slowly to a full lying position, but now it's super easy! Also when he was real small I felt like I had to hold my boob away from his face to keep blocking his nose- but with practice (and him getting bigger) it's no longer a problem. Also from Ina May, learned that by backing up a little and rolling toward him with my knee up more to keep me from rolling all the way, I can dip the upper boob down for him so he can alternate boobs w/out me having to roll over & switch sides- which is nice for nights he's extra thrash-y- so he doesn't have to be between me & Dh and pummel him awake! (or when DH is extra tired and I'm worried about him not being as alert to the little guy's location). However- that position is kinda uncomfortable as I'm then squashing the boob I'm leaning over on- but it's good to have the option.