Hemming is often one of the scariest things about sewing clothes, and unfortunately, if it is done poorly, it can make an otherwise well-constructed garment scream "I'M HOMEMADE!" I've been using this narrow hem method for years now, and it works really well for me, and I get very good results with it. This is not a "very narrow hem," just narrow. It finishes to just under a centimeter wide. I use this application on the bottom of ruffles, many skirts, and shirts. This wouldn't work well for pants or anything that requires a wider hem. I also use this same method for making narrow casings for 1/4" wide elastic for peasant dresses. Works like a charm.
Step 1: Sew all the way around the lower edge of your fabric at 5/8" and backstitch. If you're doing a casing for 1/4" elastic, sew all the way around at 3/4" instead. Doing this eliminates the need for measuring with a seam gauge at the ironing board, which I find tedious. The example shown here is a ruffle. (Note: on ruffles, hem them BEFORE gathering and sewing them on. It will save you a big headache.) I always sew all the way around again at 1/4", but you can probably get by without this line of stitching. It may or may not help the fabric fold better down the line.
Step 2: Press the hem toward the wrong side of the fabric, using your line of stitching as a guide. Make sure you press it just far enough over that the stitching is on the inside of the garment, not showing on the outside or on the edge. Press all the way around before moving on to the next step.
Step 3: Using your fingers, tuck the raw edge all the way under for several inches at a time, and press in place.
If you have to hem over French seams, you'll have a lot of bulk in the hem. Using sharp scissors, trim the seam allowance out of the hem allowance area only.
Step 4: Time to decide the best place to sew. With the wrong side up, line up the edge of your hem with the edge of the presser foot. Here my stitch is set to 1/4", and you can see that it would leave quite a flap on the left side of the stitching, so this isn't the best place to sew.
Here my needle is just a touch to the right of center. It will leave a little flap, but it's not so tiny that I'll be in danger of missing it.
I recommend turning the fabric over and sewing from the right side of the garment. Stitching usually looks best on the top thread rather than the bobbin, so you want it to look best on the outside of the garment. Start sewing somewhere on the side or back of the hem, NOT directly in the center front. Sew all the way around and backstitch 2 or 3 stitches.
As you sew, check the back side once or twice to make sure you're catching the hem.
This measurement shows how wide it finished. This is the only measuring I did the whole time!
And here is the finished narrow hem from the outside. Good luck!