If you are using sashiko thread from Olympus, pull off the paper collar and carefully find the small tied loop.
Hold onto that loop and smooth the thread out into a flat oval. Cut through the bottom of the threads. Now cut through the top where the loop you are holding is.
Best tip ever: After you cut both ends of the thread you have a bunch of loose threads, YIPES! Get someone to hold one end while you braid them together. Tie each end of the braid snugly (not tight) with a short piece of thread.
Now you can gently pull each thread out while the rest remain tidy. If the braid smooshes up pull it flat again from the ends.
I often braid several colors together. It’s pretty. Also convenient.