All graphs must have a title, all axes must be labeled including units. Wrong use of scale. Most people read increasing scales from left to right and from bottom to top. Comparative graphs must be plotted on the same axes to facilitate comparisons. Misplaced zero point.
Most people assume that the zero point is at the bottom of the graph.
This can give a very misleading impression of the amount of change present in a data series. Wrong choice of chart type. Be careful of the choice of bar charts, vs. line charts, etc. If the horizontal axis is time, a line chart is almost always better. Grid lines too dark, missing, or not relevant to the graph.