I think that the most important thing is to make a practice schedule and keep to it. If you can only practice 3 days a week, that's fine, but make sure that you never miss a practice - and that your practice sessions are worthwhile. You can make sure your practice sessions are worthwhile by crafting a lesson plan the day before each practice. Nothing major here, just a list of the things you want to practice and for how long. For example, I practice scales in every practice session, but change fingerings, patterns, tempos, etc. The night before each practice I write down (or at least think about) what fingerings, patterns, and tempos I will work on the next day. By doing this planning you will ensure that you are getting the most out of your practice sessions, and not just playing around or trying to figure out what to work on. Another idea is to study theory separately from practicing technique, as they are completely different things using completely different skills and capabilities.
Finally, don't get discouraged if you can't play as fast as Romeo or Petrucci or Gilbert, etc. They have been playing and practicing for years. Just keep to your schedule, track your progress, and soon you'll see some impressive gains.
A little hint: when practicing scales, play them over and over again at very slow tempos using a metronome. this will build endurance and strength in your fingers, will build muscle memory of the patterns your working on, it will greatly improve your picking ability and rhythm, as well as the synchronization between your left and right hands. Not to mention, it will ensure that you can play each note cleanly without string noise. When you can play a scale pattern perfectly, ascending and descending, 10 times straight then you can increase the tempo - but, only by 4-6 beats per minute. Then start the exercise over.
