Put the bow up against a wall, belly to the wall. If you can get one finger between the grip and the wall that's fine. Two fingers is ok. Three fingers is getting a bit excessive.
If you can't get both tips touching the wall, then walk away with a big grin.
Mind you've always got to ask yourself, would you rather have a bit of set or a broken bow?
Strapping the bow up with a hint of reflex and heat treating the bell works well. A good time to do it is when you notice the first hint of set coming in, or when you get it to a v low brace.
Note, most of my experience is with ELBs (English Longbows).
Del