Careful with the gridlines!
Gridlines are tricky.
As mentioned before, you need to keep your graphs clean and without clutter. The focus must be on the message itself and not the distractions or the noises. Gridlines as a general rule are a distraction and draw attention to themselves. On top of that, the typical Excel graph comes with default gridlines.
Having said that, gridlines can, used correctly, in some cases provide help into interpreting the data and getting the message in an easier way. The problem with Excels graph gridlines is that they cut through the graph area – often white area – and not through the graph bars, so apparently, the Excel default gridlines are not the solution and should be manually deleted. The example below highlights an Excel bar graph with the deafult gridlines.
Jon Peltier (peltiertech.com) has a very interesting approach to this, and uses Excel´s error bars to create gridlines that cut through the bars in the graph and not the unused, white graph area. In the example below I have used his method to get rid of the default gridlines and instead replace them with error bars. For instructions, please visit his blog.