When I first started knitting socks, the most daunting part was picking up stitches along the heelflap. I've knit short-row heels before, but I've found I really prefer the look and feel of a heelflap and gusset, so over the years I've hit upon a method that I like. There are a couple of different methods of picking up stitches along a heelflap, and it's really a matter of personal preference.
Here we have a great tutorial from Glenna of Knitting to Keep Sane, where you knit through the base of the slipped stitches and ktbl of the next row.
Here, we have a tutorial from Grumperina's archives on picking up, which I think may be the same way that I do: picking up just one leg of the stitch and knitting through the back loop to twist.
Here, I've already picked up the stitches from Needle 1, and am now working on the ones from Needle 4. As you can see, there's a lovely line of slipped stitches along the edge. If you look closely, you can see that half of the pink slipped stitch right next to the needle is twisted; this stitch has already been picked up. So, the next stitch to pick up is the purple stitch.
With the side of the heel flap facing you, pick up half of the slipped stitch with your left needle, making sure it is the half that's closest to you.
Next, insert your right needle into the back of the picked-up stitch. This step makes it so when you knit, it twists the stitch and eliminates the need to twist it on the next round.
Next, complete the stitch. You're done! Lather, rinse, repeat until you have picked up all the stitches. Not sure what "all of the stitches" means? I'll be posting a Part II with tips for picking up without holes.
Congrats! You have pretty twisted stitches and can now continue on to the foot!
I have to say, when I found this method, it made picking up stitches sort of fun. And by fun, I mean it's my absolute favorite part of knitting a sock. All the magic happens on the heel and makes a tube of knitting turn into a fitted garment.