You send me a TestFlight invite to a game or app. I start using it, i.e. the usual dogfooding method. I write down everything that comes to my mind, and send it your way, either as-I-encounter-it, or as a full-on report at the end of two days. I try to mis-use and abuse the app, if it's a game, I'll try and play it in freaky ways and see what comes up.
Basic 2 days
I'll install your app and test it for 2 days straight, writing down suggestions for UI improvements