Leo's Fortune

There are a total of 20 levels across the 5 acts, and each level has 3 stars to collect, for a total of 60 stars to obtain. The three stars in each level are obtained for doing the same three things:

1. Collect all of the coins in the level
2. Beat the level under the par time
3. Beat the level without dying

Thankfully you DO NOT need to get all three stars in a single run of a level. You can get each star on its own run if you prefer (and that's recommended too). I recommend collecting all of the coins on your first playthrough while you get a feel for the level and how to progress. Then, replay the level and go for the par time. Knowing how to progress should allow you to get the par time without much issue. Now that you've played the level at least twice, you should be familiar with the more difficult parts of it. Time to play through it without dying for the third star. 

Each of the types of stars is broken down below.

Coin Collection Stars
These are the easiest stars to get in the game. The coins you have to collect are all on the path that you're meant to follow. None of the coins is hidden in some out-of-the-way spot or behind something in the environment, so you don't really have to search out any of these, you just have to make sure you collect them all. Some are possible to miss, such as while falling or floating up. If you miss any, you can just kill yourself and then go for it. This should be the first star you go for on every level. Your first time playing a level, aim to collect all of the coins on it while figuring out how to complete it.

Par Time Stars
This is the next hardest type of star, and to earn them you have to complete the level in under the par time, regardless of how many times you die or how many coins you collect. So, while it doesn't matter how much you die, the more you die the more time you'll lose. So it'll be beneficial to be decently familiar with the level to minimize your deaths. The par time runs don't need to be anywhere near perfect runs. There is room for some deaths in each level as long as you don't waste time trying to figure out how to solve some of the puzzles or progress.

Zero Fatalities Stars
This is the hardest type of star, especially in the later levels. You need to complete the level from start to finish without dying. If you die in the middle of a level, you'll have to restart from the beginning and try again. Since time doesn't matter here, definitely take your time, especially with some of the more precarious sections and obstacles (which applies to the majority of Act 4 and Act 5). These stars will likely take a few attempts on each level, since the levels are just long enough that it's easy to make one mistake and screw up your zero fatalities run.

The video below shows the game being completed with three stars in every level, if you want to watch a level being completed to see how it's done. Even with watching a video, you're still going to need some practice to navigate through the trickier or more precarious parts. Expect to practice those a few times. 

Full credit to the creator of the video.