Simple Method:
Get a simple map that you're comfortable at.
After you have warmed up, slowly speed up the map using rate changer (external or lazer's built-in).
When you feel like you can already somewhat play the map and fc, (fc is not required, you just need to know that you can technically do it) it is time to increase the bpm once again.
Complex Method:
Get a couple of maps, they need to vary between simple 1/4 patterns like oni triplets and quintuplets, long pattern/ stream maps and burst maps, like non stream heavy patterns with 1/6.
Speed up all these maps, you will cap at different bpms on these, obviously as you can't play streams as fast as oni like maps.
These will give you variety on your speed practice and you will eventually surpass 240 bpm.
Also make sure you are not able to play the map due to being speedcapped and not reading/reaction time capped.