hmm i dont really pratice or warm up for pp, i just play tbh but i guess you could just play random maps that ARENT farm untill you feel confident enough or just warmed up in general to farm
If you mean warmup, in the ideal session I would start out with nm1 type maps (aim consistency with bursts/short streams), then move on to aim skillcap with wide/fast jumps for my skill level, then I start playing low bpm long stream maps and then higher bpm stream maps and speed/fast burst maps and then play hybrid fast aim/speed maps to push overall skillcap and by then you should be able to mechanically do most things.
Although, I usually don't actually do this and I normally just open osu and play whatever the hell I want with no regard to anything.
The gist though is that you want to start out with the aim consistency maps and the low bpm stream maps before you move on to the faster aim maps and higher bpm stream maps so that you don't injure yourself.
I personally only get pp if I farm after playing random shit for an hour or so. If I try farming before that it's just pain and suffering, you put in so many retries and so much effort for no pp.