Practice whatever you want to learn and challenge yourself to improve by practicing things you can't play. Also as far as practicing goes. It took me a year to gain enough speed and control to shred and play insane stuff like Becker or Malmsteen with much ease and enjoyment. The trick i found was working up coordination in anycase. So i would sit and practice the stuff without my electric plugged in to make it harder to make the noise audiable. Which meant playing harder to get it to sound good accoustically on my electric. Basically this is similar to playing clean through an amp but a bit harder for most electrics aren't very loud when played accoustic as in not plugged in. I figure if you can play something cleanly and audiably accoustically on an electric the transition from that to distorted will rule. And in most cases it has.
As for sitting or standing do a mixture of both practice chops and stuff sitting and then just go play it standing always remember it comes down to being comfortably coordinated with whatever you are playing. Also i susggest playing whatever you are learning slow and make sure you get a smooth solid sound to your playing unless you want a weak in feeling but technically proficient sound like Malmsteen. I also suggest trying new things and learning new tiplet patterns to improve your shredding. Don't just get stuck wtih simple 3 note per string patterns that can easily be played up and downt he fret board. Get creative and challenge yourself and always strive to work on that which you cannot do now but will someday.
Remember practice makes better not perfect. Especially since perfection is in the ear of the beholder. That and perfection is unattainable by any standard except the lowest. Practice for the ears of others to enjoy your music but most importantly practice for yourself to be satisfied with the sound coming out of your amp. Time is of the essence. Sit down for an hour and practice getting the leads or solos nailed by playing them slow and working them up. Play all exercises with extreme care listening for errors in playing. Then after an hour just play. you should be warmed up to haul-ass.
Hope that helps a bit dude.
