The Ultimate 3 Steps Leveling - level once like this and never again

After many frustrating prints, I often realized that my problem started with an unperfect leveled bed. I thought I did my best but it wasn't enough. So I digged into the leveling process and found my way I perfectly adjusted my bed (at different temperatures). I am useing an anycubic i3 mega with Marlin 1.1.9 (eg. the one brought to you by david ramiro) But the process should be the same (or at least similar) on all marlin enabled printers.

If you follow those 3 steps you will end up printing perfectly even:

1. level manually with the knobs under your bed
2. meshbed leveling
3. fine tuning (useing some G-Code commands)