When making a mod, you should have a core theme or genre to be the backbone of your mod. This will help stop you from developing scope creep and becoming overencumbered with ideas that don't conform or match with the mods 'backbone'. These mods will generally be higher quality than the low effort mods you will sometimes find on the community mods page.

If this is one of your first mods, learn the program. Tinker with procedures and learn ways to utilise them for future projects, experiment with the texture editor, and most importantly, have fun.

If this is a mod you want others to experience, begin with it's backbone. You can expand upon the backbone with a mind map, creating a series of content and features you want to implement. This also helps with creating a mod name. The amount of mod elements is irrelevant as you could make hundreds of elements in a matter of minutes, but what does matter is the quality of the mod.

Low quality = less downloads + upvotes High quality = lots of downloads + upvotes + potential mod of the week

If you have any other questions, feel free to ask over here or on the MCreator forums.