This tip works pretty well for us most of the time. I give warnings so JB is aware I will be taking a toy away or we are about to transition into another activity. I pair it with a countdown of 5 and time it so he is just done with whatever he is doing. If it is a puzzle, I let him finish the last piece then do the countdown. Most of the time this works like a charm but of course there are times where he refuses. We keep trying it and it has become a routine for us.
Another tip is being consistence and actually following through on what you say. If you want to transition to let’s say bed, you want to follow through so your child understands it is time to go to bed. A child learns very quickly what they can get away with. JB often resist going to bed but I repeat myself and tell him it’s time to go. I also give him the choice to take a few toys up with him after the warnings and countdown. For us, dragging him up is the worst possible scenario as he cries bloody hell. It’s as if he has an itch and it must be scratched otherwise he just can’t sleep. In order for the itch to go away he must willingly walk up himself.