Graphs can be an effective way to convey facts and figures quickly and with impact. However, they can also be very difficult for people to understand, misleading and leave people confusing or with an incorrect impression.
When you make a graph check that it is easy to understand. Make sure that your key point is visually prominent; to paraphrase Edward Tufte, make sure the information to ink ratio is high. The axes need to be easy to read and clearly labelled. The colours should be easy to distinguish; there is a lot of advice about what colours to use online - the defaults in most software are not that good, so think about it. Here is an example: