There are many different ways of sewing up a braid, I'll show you the methods I prefer.
In the first place I always immerse the ends of braids in a suture, if any possible. It is stable, prevents a very smooth borders from unrebelling and looks clean.When I sew the braid onto a round neckline, I steam it with a damp cloth before I sew it in form. But be careful with the temperature of the electric iron.
If I want to sew the ribbon on a dress with a v-colar, I proceed as follows:
1. Here you can see how I fold the tablet woven braid. Make sure you find a proper position, so that the pattern will fit.
2. Use long pins, when you lay the angles
3. And again the advice: try to be careful, so that both sides of the braid match.
4. Now I sew the braid together the tip of the folding. (see arrow)
5. In the last pictures I'll show you how to go on if you want a linear ending. Turn the braid around
6. Just fold the tip on the back of the braid upside. and fixit with some smal stiches.
Now turn around the braid and sew the tip together as high up as you like. (see arrow)
When sewing up the braid I always start at the tip and first fix it with some long pins. So I make sure, I still can shift the braid until it fits to my liking.
Good luck and have a little patience :-)
Below you see the work of a talented brithish museum tailor: