I cringe at bad barcharts and line graphs even more than I do at bad grammar. When someone just uses an awful default graph in Excel that could have been made so much more visually attractive with minimal effort, I want to throw something from the audience.
Of course, tip number one is to use the right chart in the first place. Line graphs are for time series, and are designed to show trends. It may not be necessary for the Y-axis to go down to zero if that makes it harder to see the trends, but if that’s the case, make sure the Y-axis values are shown prominently. Vertical barcharts (or column charts, where the bars are vertical) can also show time series, but are more for comparing values, and should really have the Y-axis starting at zero. In fact, vertical barcharts are preferable whenever the X-axis variables are numbers, or groups of numbers, and have a natural order, left to right. Horizontal barcharts are better when the variables are named items. This style of chart allows you to order the bars any way you want, top to bottom. Normally you’d put the most important bars at the top.
As for styling, be ambitious. Search for some barcharts and line graphs using Google Images and find something attractive, then copy the ideas. It’s surprisingly easy in most spreadsheet applications. Avoid gimmicks like 3D – there’s a reason professional graphic designers rarely use these. But backgrounds don’t have to be white, bars don’t have to look all skinny and sad, and points on graphs can have nice markers. You can do it.