By virtue of their electrical properties, tubes generate a special waveform when they're saturated, which is why tube engineering has tremendous tonal advantages over solid state or DSP solutions, particularly for crunch and lead sounds. Tubes enter the saturation zone gradually or softly, which lends tube-driven tone its trademark yet totally unique character.
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What do you know already ? I'm guessing you know a fair amount of theory after 5 years of playing. Do you play in a band ? That will help your rhythem if you do. Also it depends on your weak points. Try and work on anything your not to good at. I'm not really sure what else to say because i dont really know what you know already. If you have all day to practice you could just search sites for lessons and try and find out what people like steve vai and brian may would practice.