The main problem I see in students is their LH wrist position. 70-80% of the time, a straighter wrist is best. Lots of beginners (and more advanced students!) have trouble getting their fingers down in the right positions, and default to their wrist suddenly bending to straighten their fingers and allow them to put the fingers down perpendicularly to the fretboard. This is usually the opposite of what is most relaxed, which is to relax the wrist, keep it in a 'neutral' position, and curve the fingers more so they come down onto the fingerboard like little hammers. By going the 'wrong' way, we open up our fingers to collapsing joints. If you feel your fingertip joint collapsing often, this is probably why.
One other thing that I'm guilty of (but working away from now I've noticed it), and many others, is letting the hand tilt so the pinky finger knuckle is further away from the neck than the index finger knuckle. This means the pinky flaps at the fret you're aiming for losing control. This caused some fairly scary times for me when I got nervous and things went really bad in performance, with my hand going further and further into a bad position with me thinking it was helping. Glad I've noticed it now though!