Study the courses on YouTube for all the shortcuts, start with one course and master it, then the next one in the cup and when youve nailed all four in a cup, make sure you play that cup with your child, you can also change the aggressiveness of the cpu but we don't bother.
Learn how to master gliding round the corners and getting sped boosts from players in front of you.
Dd always saves the boom box thing if she gets it as it's can prevent a flying shell that hits the person in the lead, from taking you out. It's the only thing that can I think and she's always in 1st so she saves it.
Ten coins will give you a small speed boost.
The steer assist thing I don't like and play better wjth it off, dd leaves hers off too.
Practice practice practice. I carry my switch about with me instead of a book for bus rides etc.
Bananas I keep on the back of my car because a red shell won't hurt me and takes the banana instead , if you hear a bullet coming behind you move to the edge of road so it doesn't hit you. if I get the star I take out as many people as I can and go over the grass as you don't slow down when that's activated.
Also my fave when I pull it off, if you're in first and other players are close and there's a flying shell in its way to you, I drop back so the flying shell hits first player and I don't get caught in the blast, if you're second and hear the flying shell coming the person in front, give them space so you don't get taken out in the blast radius and if you're in third and it's a close race, you can sometimes whack second place into the blast radius.
If you're playing in split screen on the tv, save things like the squid or lightening until you can see the players in your house would be inconvenienced the most, the lightening is great when they're about to do a jump, the squid is great if you can other players approaching a load of bananas.