When nail care is done seems trivial, but it can have a huge effect on playing and your practice day.
When NOT to file your nails
In the middle of the practice day. Don’t file your nails in the middle of a practice day. A little smoothing of the edges with sandpaper or something similar is okay (micro mesh pads make this easy), but try to avoid reshaping mid-day.
Over the past few years, I’ve found that shaping my nails either (1) the night before or (2) before starting to practice gives the best results. Shaping mid-day makes me feel like I’m starting all over again, and I have to get used to a new instrument before I can really start practicing again.
Take care of your nails before you start practicing for the day. Just a simple thought to make your guitar-life a bit easier!