Probably the best onboarding to a game I’ve seen is Alto’s Adventure, you start the game, then bam, you’re playing.
I like that.
I’ve tried to do something similar in Trainwreck, The game loads the onboarding level and the train smashes through the Logo, it gives you one option, tap the signal. If you can tap that signal, you’ve learnt how to play the game.
It then moves you onto the next part of onboarding, showing you two signals, the aim is to get the train from the left side of the screen to the right side without getting hit by the other train.