Spam the A-button like it owes you money.

Some of us bring the controller up to our face when we're mashing which helps for some odd reason.

Hold left on the thumbstick when you're mashing through dialogue with a <Yes/No> choice in it to instantly select the "Yes" choice and never again choose "No" by accident.

In Deathball however, be careful, after the 2.5 minute 'running passes with Jazz' session, if you accidentally say "Yes" to her when she asks you for more practice, you'll be loaded in for another 2.5 mins, and won't be able to exit it until it's done. For this part, don't hold left, just leave the thumbstick in the default position when spamming here.