the musical klutz method is what i use. i may have a midi song already that i want to add a part to or i may want to replace a particular instrument.

as a keyboard player i'm really bad but with my midi controller i can transpose the keyboard so that the white notes (the key of c which i can find my way around) can become any key I like so that's no problem for me to record a midi track. then if its a bit off I can quantize it anyway. or if there is one bum note or just a couple, i can change it in editable notation.

as to bits being too fast, simply change the bpm to a lower speed and then return it when you've recorded the part.

don't forget you can record parts in easy chunks