I usually have someone to help me!!
I have done it single handed like this (
), but I quickly chuck the painter over the winch post and tie off, and then switch off the engine before hooking up and winching in to secure properly.
The boat tends to lift the nose out of the water quite a bit under power, so when you tie off with the painter and then switch off, although the boat does try to roll back down the rollers it is still held in position quite securely.
So far, anyway......
For peace of mind and just in case, I usually have an extra pair of hands available to help out.