Some bad habits I see most are inefficient left hand techniques. One major part of this is applying too much unnecessary pressure to chord or finger notes. You can easily tire out your hand if you are grabbing each chord with maximum pressure and you'll also effect the quality of the notes you are fretting.

For a practice exercise, place your finger on a note as you normally would. Let's try the 3rd fret of the 6th string. Try to remember the amount of pressure you use to play that note. Now take your finger off and then reapply it only this time gradually apply pressure until the note rings out clearly. Remember the difference in pressure that you normally use and what you actually require. Practice this all over your fingerboard and see if it doesn't make a difference in your playing.