They already pointed you to the guides, so I guess I'll try to give some tips for actual practice.
You should look to doing these as practice (while watching the guides everyone suggested):
1.
Just choose a random map then try placing stuff like a real map. Doesn't have to finish, be good or whatever. Just start out.What does this do? It helps you get used to mapping, brainstorming, ideating, struggling, failing, and choosing how to map a certain sound, a section, a song, music. No rights, no wrongs. Map like you're trying out some new art materials.
2.
Choose a mapper whose style you like. Ideally, someone who has a simple mapping style full of simple shapes and is clean. Ideally, someone who has a ranked map. Ideally again, someone whose ranked map is a song you like. Then, choose a ranked map of theirs which you like.
Then, try mapping the song of that same map. You could recreate the style, maybe. You could make your own twists that you like which you thought, "ah , this is better," maybe.
What does this do? It helps you understand how mappers think. The fact that a map is ranked means it's
generally considered good and acceptable in most people's eyes, and the mapper behind it has decent enough standards. It helps you gain mapping standards and beliefs.
"Why did my fav mapper put this circle here? Why did he make the slider shape like this? Why is it blanketed? Why is there a jump here? A stream?"
"Ooh look at this pattern, it's pretty interesting. Can I use it in another way?"
"This map was ranked, approved by at least seven other decent mappers, so it has to be somehow good, right?"
"Couldn't this circle be here instead? Couldn't this slider be straight instead? Couldn't we have used a flower slider here? A spinner instead?"
Through this activity, you should be able to come out with
at least a section of that song mapped by you. Don't try to finish it if its hard, maybe just focus on the chorus or the instrumental or the intro of that song. Like #1: doesn't have to finish, be good or whatever. You should also come out with an understanding of why people like and allowed to rank a certain map.
In no way are these the widely-accepted steps to actually become good in mapping; in fact some might disagree and say this is hard. There are many ways to go about learning mapping. This is just one suggestion.
There are also some things which you will have to re-learn after taking these steps, and it will not be straight. For instance, you might find that others still disagree with your map. Some of the things you learn in #2, for example, may be rejected by others. You'll just have to re-learn things afterwards and decide for yourself what's the right answer; you'll have a somewhat guided mapping sense by then, anyway.
By the way...By the way, I saw your top scores. Some of them have songs which are good, like Miraizu and Kawaige Nai na. Didn't look at the maps themselves, but maybe, just *maybe* you could look to try making a map on those for #2.
Also...I can point you to some good mappers to reference for #2, hit me up in DMs.