Do not leave the instrument in the car, even for five minutes. The heat is very bad for the instrument and can result in a crack (not to mention theft). Make sure to store the instrument in its case when it is not being used to prevent it from getting knocked over or any other type of damage.
Use the fine tuners. Avoid using the pegs to tune unless absolutely necessary.
Don't touch the bow hair with your fingers or it will get dirty. Always loosen the bow when not in use. If you do not loosen your bow, the tension will cause the stick to warp over time. When loosened, the hair should touch the stick. Do not loosen so much that the screw becomes loose, however. Do not over-tighten your bow. The stick should never be so tight that it is straight or curved away from the hair.
Always clean your instrument after playing to remove excess rosin dust. Over time, the dust can build up and damage the varnish of the instrument. Use a microfiber cloth to wipe away rosin dust. Clean the stick of the bow as well as it is treated with the same varnish as the instrument.