I pinch and mark the center of both pieces, pin that and then the ends. I pin anyway, and I pin a lot on curves filling in by quarters from the middle and sides. Generally it curls up in a ball as I sew but I can't swear on which side I put on which way.
Although I generally press open, curves are the only time I press to the side.
I do everything I can to avoid handwork but I'd say that curves like on a drunkard's path are probably best done by hand below maybe about a 4" final size. Sure you can (and I have) machine pieced smaller ones but there are diminishing returns.
Melon shaped arcs aren't much of an issue for me, and grandmother's fan sized ones are relatively easy as well. However, this past year I used what I call the "Eleanor Burns Technique" using rickrack for the curved edge and I really liked it, it added texture and interest to my project and was very easy to use. I think it starts around 18-19 minutes into this video:
https://www.youtube.com/watch?v=Ktzb2wMMwzc