During my teaching sessions I often see students (beginner level) struggling to keep the hem folded while they can sew it and for obvious reasons they do get stressed. So here are few tips and techniques that can help you hem comfortably making the whole process enjoyable and relaxing.
1. Pinning: fold the edges using the pins and then hem.
2. Tacking: fold the edges and do a long distant running stitch on it with a single thread. Once you are done with the hem simply remove the running stitch by pulling the end thread!
3. Ironing: you can fold the edges and iron on it. But this technique is more useful if you are dealing with a cotton fabric.
4. Fabric glue: there are lots of brands in the market like Sewing box, Quick sew etc. that would easily hem folded while you sew them.