Save your donuts for cases when you really need them. If you can use a donut to grab another one, that's a net gain.

Buy new items as quickly as possible, and that's especially true of the snorkel. Unlock it as soon as you have the opportunity and use it to dive into the water for easy donuts.

Go for distance, not height. Sticking to the lower levels often will make it easier to manage a decent run, since a lot of the boosters tend to appear at lower elevations.