On glyphs like P, I don´t rotate, just pull the points down til it looks good

I’m a user of this method, but only on the round characters, those with horizontal stokes never get rotated and need more manula correction, though less than if they were rotated and then you had to fix ’em.

IMO you have to develop an eye (and hand) for tweaking these curves manually.
One method is to mechanically slant your roman type, then put a similar glyph from Helvetica, Futura, whatever, in the mask layer, and see how your BCPs and handles have to be moved to get correspondence.
Note in particular that the extrema “slant line” in many faces differs for curved and straight letters, and may even vary between O and S.
Looking at the shapes sideways, upside down, and back to front also helps.

For info see also the ’How To’ Typowiki, and in particular the Obliques How-To. This has a more extensive description from David Berlow, plus links to other threads.