"how do you practice" - normally i sit in a chair when i practice. for a 4 hour minimum, a padded seat is a must.
a developed my own 10 hour plan, similar to steve vai's i suppose, but more personal;
hour 1 - chromatic speed studies
2- scalar patterns
3- break it up a bit with some reading
5- play through tunes from my repertoire
6- work on new techniques (i'm working with country/bluegrass now, so banjo rolls, chicken pickin', etc.)
8- read up/apply some theory
9- improvise (plus whatever improv happens in hour 5)
10- anything that needs extra attention.
i try 2 hours, then 1/2 hour break, and continue the cycle.
yes, before anyone asks, i do have a job