I use different licenses on different projects, but you should know a little something about the licenses and what type of rights/permissions they give you so without further ado:

CC By-SA 4.0 (I use this most)

This license gives you permission to download and reuse, modify and share resulting work, or the original work. You MUST give proper credit, and if you modify the file the resulting file must be made available under the same license. An example of this credit would like like this: (file name) by Nathan Salapat is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

You can learn more about the license by clicking on the link. (file name) should be replaced with whatever the file is, and Nathan Salapat should link to my website, www.nathansalapat.com anytime you use a file for something this information should be included.

Non-Free (I try to avoid this)

Just as the name suggests, the file isn't free, technically you shouldn't even download it. I probably wouldn't even provide a download link. You most certainly can't use it for anything, and may not modify it. Most of the time that I use this license will be paid freelance work that I'm only showing for people to see what type of things I can do.