Mastering lines, sideshift and pitch are some essentials to fast times, anticipated decision between a speed or weapon pad, wisely using your shield energy (don't waste it on a not very beneficial roll when you are low for example), being able to pull off ALL shortcuts and having the descipline to save a turbo until a shortcut opportunity also add to that.

Not to self promote, but for the whole lines thing, i do have a guide thingy ma bob on my youtube if you want to check it out, it's a lot of me rambling though, but the slowmo example lap with button input might be of use if you decide to skip the other parts
Link: https://youtube.com/playlist?list=PL...JJeaSaeLvSeXOk