Maybe these shouldn't be asked.You can see my first blog and I'm joked as you.No one replies seriously.The peole here are mostly just like that.

more practise

1- Solve more problems

2- depending on what you mean, if you mean become faster at just writing code, then you can practice touch typing (try typing club or something), if you mean reaching the solution faster, then refer to the answer of the first question (You usually reach the idea faster if you have solved something similar before, solving more will surely help on this)

3- You are asking in the wrong place, usually we don't focus on writing a clean code in a contest because we need to write the code quickly, it's not easy to write clean code quickly, I can give you some general tips like "use meaningful names"... etc, but I would suggest googling since there are a lot of clean code practices that I can't be written in a single comment, You may even read Clean Code book.

For CP, just try to keep everything idented correctly and maybe divide the too complex logic into smaller parts (functions or just separating them by a line or something to make debugging easier)

4- Refer to the answer of the first question

The 'science' of training in competitive programming by I_love_Hoang_Yen

reach red and u will be able to do that