There are just a few basic techniques that you need to know to be able to mend just about anything. The rest, to me, is about combining these techniques and experimenting! This post is about reinforcing fabric around a hole by hand by attaching a patch to the back (under) side of the garment.
This underpatching technique works well with non-stretch fabrics in any weight, though it can easily be modified for something stretchy. You can change up the colour scheme to make your stitches more or less subtle against the garment :):)
1) cut a patch to fit over the entire hole or worn/threadbare area: in this case, there were just two small holes with no sign of wear around the holes
2) pin patch in place
3) optional: tuck the raw edges under and pin in place: here, I snipped the holes bigger in order to get the seam allowance to turn under! I could have cut even bigger to reveal a clean rectangle for a different look.
4) stitch stitch stitch! the specifics of this are up to you. I went around the hole in whip stitch (green)
...and then echoed the stripes with running stitches (pink).
I could have gone more minimal with just the whip stitch + a round of running stitches around the holes, or if I hadn't turned those edges under I might have omitted the whip stitch altogether! Or, I could have trimmed the holes square and tidy rather than the abstract amoeba shapes. This technique is very adaptable and I use it all the time for a result that is both strong and beautiful. Would love to see your take on it!