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@SSD The easiest way is to increase the difficulty of your level so that the gameplay is entertaining/intricate enough to get a 5-star rating. The drawback is that your average rating counts may decrease as some players like playing relaxing levels (like me )

The second way is to increase the originality of your level. Not only can this increase your chance of getting a 5-star rating as the difficulty will become secondary to players, your level may also become more popular due to non-standard gameplay. Check out @Denis Nazin's Playing Cards for example. You can see its gameplay is easy, but the concept alone is just worth 5 stars

The third way is to improve the design of your level. Some players may add an extra star for this factor! If your design is great enough to become a visual masterpiece (check out @97 NinetySeven's levels), you can get 5-star ratings without gameplay. However! There are 2 drawbacks to doing this:
1. It is relatively time-consuming
2. Some players may not take design as the prominent factor when rating your level

The final way is to include discoveries in your level, which is the hardest thing to do, but you will be rewarded 5-star ratings for sure! Check out @Labyrenight's Fingertip 2 as an example.

Hope this helps