When you're first learning statistics, visualization, or any data-related subject, the data usually is given to you in a ready-to-use format. This is so that you can spend most of your time on the topic of interest. But once you step outside the learning bubble, data rarely comes in the format you want.
Marc Bellemare, an associate professor in the Department of Applied Economics at the University of Minnesota, provides some practical tips on how to deal with this. Bellemare's parting advice:
Really, there is no big secret to cleaning data other than "Document everything" and to save everything in different files and in different locations (i.e., your computer, Dropbox, Google Drive), and there is no other way to learn data cleaning than by doing it.
Some of the tips are in the context of specific software environment, but you can easily apply them to more general situations.