Gaining height
Go up to higher platforms to find most of the ghosts, the special cookies (fruits, etc.) and a better chance to continue. Falling from great heights will not harm Pac-Man.
Power-ups
Use power-ups only when you have to, for example when you are close to completing a mission. Besides cookies, purchase Cylindria or Spiral as soon as possible to allow Pac-Man to double jump and collect off-screen ghosts. They are very useful in missions where you need to eat many ghosts to extend your time. The spinner versions of these power-ups are a lot more effective. Do not bother with the Magnet ones, as their area of effect is too small.
Various Tips
The distance Pac-Man runs contributes to how many cookies he receives at the end of each level. Save those cookies to buy different items in the shop. As in most games different characters come with unique abilities that help make the game easier. Make sure you choose the correct item to complete missions. If the objective involves dashing a set number of times, equip Dash. If you must eat a lot of ghosts, go with Cylindria. The game will let you know if you're prepared beforehand, which prevents you from wasting Stamina. You can always replay previously completed missions to get more cookies. Eat as many ghosts as possible to add precious seconds to the clock. Keep in mind these ghosts grow progressively quicker. You may need to jump to devour the trickier ones. Keeping Pac-Man in the air for extended periods of time will quickly deplete the clock. You'll know you've completed an objective when a medal appears at the top right corner of the screen. Perform well to earn Clear Bonuses. Make sure you choose the correct item to complete missions. If the objective involves dashing a set number of times, equip Dash. If you must eat a lot of ghosts, go with Cylindria. The game will let you know if you're prepared beforehand, which prevents you from wasting Stamina.