This is one of those how long is a piece of string q's - the simple answer is that there is no one guaranteed way that will work for everyone.
However, based on my own experiences I would say that the following will give you a good basic level for most styles:
Intermediate Level Targets
Scale/Arpeggio Knowledge
Minor, Major Pentatonic 5 positions
Minor Blues in 5 positions
Major (Ionian) Position 1 + 4 plus 3 note per string Root 6th and 5th
Minor (Aeolian Ionian) Position 1 + 4 plus 3 note per string Root 6th and 5th
Dorian Mode Position 1 + 4 plus 3 note per string Root 6th and 5th
Mixolydian Mode Major (Ionian) Position 1 + 4 plus 3 note per string Root 6th and 5th
More exotic stuff like Lydian, Phrygian, Harmonic Minor etc arent as commonly used as the above so deal with them later!
Major, Minor, dim triads 2 string root 2nd (a la Hotel California/Final Countdown/Sultans Of The ) and 3 string root 3rd
Major 7, Min7, Dom 7, m7b5 - ideally root 5th and root 6th spanning two octaves.
All of this will give you the core basic knowledge - then you need to be able to apply them.
A basic technical facility should include:
Being able to alternate pick these ascending and descending in 1/8th notes to approx 170 BPM, triplets to 140 sixteenths to 100, sextuplets to 80.
Phrasing ability to include:
Bending Vibrato sliding legato hammer ons pull offs tapping pick harmonics
A core knowledge of a couple of dozen classic rock/blues licks in position one.
Armed with all of this you should then aim to learn a couple of dozen classic solos (and all the rest of the song of course!) as the best way to gain an insight is to study the masters...
Then you simply combine all the above and gradually you will develop your own style.
Cheers
Owen
http://www.harpercollins.com/authors/35834/Mr_Owen_Edwards/index.aspx