In actuality, mascara ought to be thrown away after three months. You might think that's too fast, but experts are really just thinking about the health of your eyes. Keep them clean and in tip-top shape by getting rid of products when it's time.
Also, don't pump the wand in your mascara to get more product! This just causes the formula to break down faster, and introduces air into the tube, breeding bacteria. Instead, gently twist the brush before you pull it out.