Leveling Up
Mario gets to choose whether to gain five Heart Points, five Flower Points, or three Badge Points each time he increases in level. Mario will increase all of these to the maximum value at level 27. The order the stats are chosen can affect how difficult the game can be. Heart Points serve as health in the game. Mario gets attacked most of the time, so he will lose Heart Points faster than his allies. Initially the enemies are so weak that this is not an important stat to focus on. Flower Points are used by Mario and his allies to use special attacks. The starting value of five Flower Points is so low this should be the first stat you add in your first few levels.
Badge Points are more versatile than either Heart Points or Flower Points. Once Mario starts getting Badges, this should be the focus when leveling. Mario can use three Badge Points to gain five Heart or Flower Points, so you can get the benefit of leveling Heart or Flower Points for Badge Points. In addition, Mario can gain a wide variety of abilities by using Badge Points.
Badges
Mario only gains a maximum of 30 Badge Points during the course of the game. This is far fewer than the amount needed to equip the majority of badges in the game. A whole range of different badge combinations will work effectively in the game. Usually, the most effective badges are ones that focus on one aspect of Mario. What type of focus is up to the player. One player might focus on gaining a wide variety of different Jump attack badges and badges that help power Jump attacks. This gives a greater range of different types of attacks for Mario to use. Another player might only take two Jump attacks and spend the rest of the Badge Points on Flower Point upgrades and Jump upgrades. That player would only have two attacks, but could use them as effectively and often as possible.
Easy Star Points
Normally, enemies stop giving experience points once Mario reaches a certain level. In order to keep leveling, the player must advance to a harder zone. The Amayzee Dayzee in the Flower Fields is an exception to this rule by always giving at least 40 star points. This makes it easy to amass the 100 star points to level quite quickly. In order to reach the Amayzee Dayzee, you will need to use Lakilaster to cross the spikes on the bottom right path. You have only a one in four chance it will appear each time. Travel back two screens after killing it or if it doesn't appear to cause it to respawn.