A string is like an elastic band. At some point the string will have lost it elasticity, by that time the string will no longer feel slippery (typical feel of new strings) and it is time to change your strings. To avoid breaking strings during your playing make a habit of changing your strings regularly, all depending on how often you play and your playingstyle, but changing strings regularly will make sure you keep that fresh feel under your fingers and avoid embarrassing moments of snapping a string while in the middle of playing a song.
Sharp Edges on Bridge or Frets:
Sharp edges on either bridge or frets appear as part of wear and tear on your guitar, they can cause a string to break. If you break a string often at the same point check to see if you have any sharp edges on either frets or bridge. You can smoothen out those rough edges with some fine sandpaper or a fine file. If you do not trust yourself with any of this check out your local guitar repairman.
Your Own Technique:
You may play too rough for the strings to handle your playing style. Work on your technique to smoothen things out. You do not need to be gentle on your strings, they can handle a lot, but it depends on how you strike the strings. You can sometimes notice differences when you change your tecniquqe. There may be a point where you break strings, because you strike the string harder than how you used to play before. In cases like this try to smoothen out your playing, over time you will learn how hard to attack those strings. If you still keep breaking strings learn to live with how you play: change strings often for them to keep up with your style!!
Floating Tremolos such as Floyd Rose Systems:
Heavy use of trems like the Floyd Rose will wear your strings out quicker simply because there is more movement of the strings. Again, as what I mentioned before about your own technique, breaking strings while using any floating tremolo system will depend a lot on your style: It may be possible to use your trem all the time and not breaking any strings at all.
Changing strings all depends on your style and preferences: Some guitar players do not like the sound and feel of new strings, therefore they may be quite happy not to change them too often. Most of use like to keep them fresh, and to achieve this changing your strings from time to time will help you!
Have a Great Time and hope to catch you soon again,