The best way to create just songs for your NANO is to create a Smart Playlist for it.
Select each song, individually, in the Library that you would like to have on your Nano, and once it is selected, go up to the File and select "Get Info"
Select the Info tab in the Get Info box for that song, and under Grouping type in NANO then click OK
Repeat this for each song you would like on your NANO
Next, Create a Smart Playlist by going to the File option and selecting "New Smart Playlist"
Make sure that the "Match the Following Rule" is checked, and in first box, select the down arrow until you find "Grouping" and select that
Leave "contains" as is
In the next box type in NANO
Uncheck the "Limit To" box
Leave "Live Updating" checked
Now, hook up your NANO to your computer, and under the Music tab for the NANO, check "Sync Music", "Selected playlists, artists, albums, and, genres"
Below, under Playlists, check only your NANO playlist and then Sync
Couple of notes:
You can change the name of your smart playlist by just clicking on it in the Playlists section. When it highlights purple, type in whatever name you'd like
As you add new songs to your library, you can always add them to your NANO Smart Playlist by going to the Get Info option under File, and simply typing NANO into the Grouping section. This will cause it to automatically add it to your NANO playlist!
I know this seems like a long set of instructions, but in the long run it really saves time, and also keeps your music where you want it to be. Smart Playlists can be applied to any of your devices in a very large array of combinations!
I am no music expert as far as this stuff goes, but with two people sharing the same library and multiple devices, I have found that this method works great for me!
Hope it helps you too!