Changing strings
Depending on how much you play and which strings you use they will probably need replacing every half year or year with your e-string needing replacement more often. Gut strings need replacing most frequently and steel strings last the longest. Change strings that show obvious signs of wear like loose windings, corrosion and flat areas. Strings that are getting too old will also start to sound dull or the fifths might be out of tune. When you change strings, change one string at a time and keep an eye on the bridge, it will probably bend forward a bit. Rub some graphite from a soft pencil in the string grooves in the bridge and upper nut, as it makes the strings slip through the grooves more easily. When tuning the new string up avoid tuning it up too high, it can snap. This happens especially easily for some cello a-strings. Finally, if a new string keeps breaking make a note of where it snaps. There could be a rough spot in one of the string grooves, the fine tuner might have a sharp edge or it might rub somewhere in the pegbox. As with straightening your bridge it's probably best to have someone show you how to change strings for the first time.