Why Line Charts?
Usually there is no need for a grid although they can be useful. You’ll want to think carefully about the interval of your ticks and ranges. You don’t want too flat of a line, nor too steep of a line, usually 2/3’s ends up a good range for the line chart.
If you have multiple lines on one chart, you’ll want to distinguish them as separately. Color is good, but shade might even be better. It’s even better if you can throw the label (usually in the legend) right on the line, it makes it really great.
Small multiples might be useful as well. Small multiple is a term coined by Edward Tufte.