No matter what you are working on or whether you are a beginner or a pro, you always have to practice under the same 4 guiding principles:
1) Sound Great!
-- It doesn't matter if you are just starting out. You need to make sure that every note you play sounds great. This is true at every tempo! That means no buzzing, no dead notes, no scratchy sound with the right hand, no popping sounds. You really have to listen to yourself.
2) Stay relaxed
-- Tension is your enemy! Make sure you are NOT pressing too hard into the fret board. And make sure that your left hand fingers are NOT pressing into each other.
-- Make sure your right hand is not digging into the guitar.
3) Be Precise
-- Always make sure your left and right hand fingers are planted precisely.
-- Always make sure your arm, wrist, and body postures are correct!
4) Play with Dynamics
-- Many people make the common mistake of saying, "Once I get the technique down, then I'll work on dynamics." This is like climbing 3/4ths of the way up the mountain and then walking down 1/4th of the way just so you can head to the top. Dynamics are crucial to performance and should be practiced from the very beginning. Empirical research on skill acquisition has shown that practicing a skill with variability (e.g., dynamics) decreases learning time and increases precision!