Theme: While I believe almost any theme can be successful, choosing the right theme for your skills and imagination can make the map a lot easier to create.
Terraforming: Whether it's a focus of the map or not, there needs to be at least some to make the map look natural.
Overall Build Style: Your builds need to fit the theme, be unique, and have variation in blocks used within them and the building shapes throughout the map.
Tiering: Now map makers have a good degree of control over this, so it's important to try to put Tier 2s in logical places and fairly spread out.
Gameplay Orientation: You need to build your map keeping gameplay in mind. Make sure there are at least some open areas, but try to make the map layout interesting vertically or some other way to encourage alternate combat styles and strategies.
Overall Precision: Make everything look good. Don't be afraid to change things. Keep your terraforming and building sharp and don't have sloppy mistakes like accidental asymmetry or weird terraforming spots.
Corn: This is the first thing people will see. Make sure it's fair and good-looking. Don't be afraid to try to innovate! I worked on Vida Cova and I really like how the corn works for combat.
(Optional) Deathmatch Arena: If you decide to make one, make sure it fits the theme still. Keep it fair and try to do something that makes your arena unique in design or layout.
That's all I can think of for now, I'll add anything if I think of something else.
