You should not skip values when you have numerical data. Use the full axis and do not skip values when you have numerical data. The trend is distorted if you do not have even intervals between your dates. Make sure your spreadsheet has a data point for every date at a consistent interval, even if that data point is zero.
The x-axis in the "wrong example" below has a time-series with inconsistent intervals giving a distorted view of data over time.
Simple, straightforward titles attract viewers. Include a short title that either describes the data (for example, the relationship between voter turnout and weather) or the specific pattern you wish to show (i.e.: estimated number of potential voters deterred by rain or snow on Election Day).
See more: Tips for Writing Great Chart Captions
Using color categories that are relatively universal makes it easier to see differences between colors. The more colors you need, the harder it is to do this. But different colors should be used for different categories (e.g., male/female, types of fruit), not different values in a range (e.g., age, temperature).
Adding too much information to a single chart eliminates the advantages of processing data visually; we have to read every element one by one! Therefore try to avoid the use of pie charts when comparing a large number of items. Simple pie charts displaying 2-5 categories may work just fine, but when displaying more data it is better to choose another chart type, most often bar or column charts will be a much better alternative. Or remove or split up data points, simplify colors or positions, etc.
Below you have the same chart displayed as a color-blind person would see it.
If the chart is readable in black and white than it is even better!