A. The most common cause of strings snapping before their time is tuning them too high. Using an electronic tuner will sort that one out. You should also consider whether you're fitting the correct gauge of strings to suit your playing style. Heavy-handed players should avoid extra-light strings. If your guitar is fitted with a locking top nut, make sure that you're not tightening the Allen bolts too much. That can break strings too.
Examine the broken string to find out which end of the guitar is responsible for the breakage. If the string snapped at the headstock end, examine the machinehead posts for rough edges. Smooth down rough parts with some extra fine sandpaper. If the string breaks at the bridge, check the saddles for signs of wear or rough edges. Running your finger over the area that normally contacts the string should do the trick. Again, fine sandpaper will tackle the rough bits. If the saddle is too badly worn to repair, bite the bullet and buy a new part. Try www.allparts.uk.com.
Finally, try swapping the bridge saddles around to see if the saddle is to blame. For example, fit the B string saddle in place of the E to see if the string still snaps. It's a bit fiddly, but it will help you isolate the cause of your snapping strings.