James pretty much summed up the important things. The most important things are to have a practice goal, and practice every day.
I also like to add technical exercises to my routine to help with hand strength and dexterity. I'll run scales for an hour until my hand cramps. I'll take a break, and then run scales some more. This sounds like work, but I know that the payoff for it is me becoming a much better player, so its actually fun and rewarding.
These are some of my common practice goals and specific exercises I like to do.
Technical: Scales and arpeggios. Picking technique. Hand stretch.
Theoretical: Learn a new key pattern. Write a ditty in a specific key. Find all of a particular note or chord on the fretboard. Learn all of the chord voicings for a given chord. Circle of Fifths.
Compositional: Learn a new song. Write a new song. Practice common chord progressions.
And it's all fun. Having an instrument in my hands makes me happy.