A presentation slide is like a photo, or like a painting: the basic rules of composition apply.
  • Rule of thirds. Put your screen guides so that they divide the page in 3-s, creating a 3x3 box of 9 rectangles. Place and align objects alongside these lines
  • Balance. Make sure charts don't "tilt": heavy graphical objects one side of the chart should be compensated on the other. If the slide is out of balance: move things around or give them a lighter color
If you are interested, read more about the Golden Ratio and use it instead of the Rule of Thirds.