One of our fave finishes is the Flat Fell or Felled seam. It's easy as heck to do, and makes your work look amazing in just a few easy steps.
1. Sew your seam (right sides together). You can do this at 5/8", but your flat fell will look even better if you start at 3/4" So, if you know in advance that you'll be sewing a flat fell, give yourself that 1/8" extra when you cut.
2. Press your seam open.
3. Trim the seam allowance on the side that you want your seam to "fall."
4. Press the other seam allowance over the trimmed one, and turn under 1/4"
5. Sew the seam allowance down as close as you can to the folded edge.
This seam has a zillion uses! Most men's shirts are flat felled on many seams. It's a little more challenging to do on a curve (I probably wouldn't use it on a princess line seam), but if you're setting a sleeve in flat (another tutorial coming on that one!) you can usually pull it off.
It's great for inseams or out-seams on pants - jeans are usually flat felled like crazy! - and I use it all the time when I'm making scarves. It saves you money if you cut your scarf fabric cross-grain, and sew a center back seam. But you sure don't want seam allowances showing, so a flat fell is the perfect solution!
Here's our video tutorial: