Here’s a quick and easy smart playlist for you. Let’s create a collection of only songs released in the 90s. This is a very simple playlist, and its utility is primarily as a component of other smart playlists.
In iTunes click File → New → Smart Playlist …. Then choose the parameters set in this screenshot:
Of course you can change the years to choose songs from a different decade. Or you can add a star to the Rating setting if you want to make it a Greatest Hits playlist.
And don’t forget to read how to create an Ignore playlist!