Tip for fastest level up, before level 45:-
In the first 3 days, all radicals must be answer correctly. Kanjis correct or not doesn’t matter. After the 3 days, all Kanjis must be correct until Guru.
As long as it is apprentice or unstudied, you can study the item as much as you want. Just make sure you remember before relying on the SRS. A good weapon for this is either Anki ( https://wanikanitoanki.com ) or rfindley’s Self-Study Userscript.
My approach is pre-studying level+1 on Anki, both Kanji and Vocab, f*ck the radicals (I override them).
Tip for after level 45 (excluding level 48) is, 90% or all of Kanjis must be correct all the time.
Accuracy is very important. Remembering for the first time is very important.
Forgot to mention [Userscript]: WaniKani Ultimate Timeline. This too is important for perfect and fastest leveling up.