When you plug an iPod mini into a computer that bears an iTunes library larger than the mini's 3.7GB capacity, iTunes offers to create a playlist that contains a subset of the tunes on your computer. This is a very cool feature, but not as cool as it could be. You see, when iTunes creates that playlist it gives no consideration to file size.
For example, the resulting playlist may contain a selection of the tunes you've created in GarageBand—AIFF files that devour 10MB per minute of stereo audio (AAC files encoded at 128Kbps are about 7-percent of this size). Because the mini's storage capacity is limited, you must bar such files from being automatically placed on the mini if you want to approach mini manna (1,000 songs in your pocket).
To separate the storage-hungry wheat from the chaff, create a Smart Playlist with these conditions:
Enable the "Match ALL of the following conditions" option.
Kind is not AIFF audio file
Kind is not WAV audio file
Kind is not Audible file
Kind is not QuickTime movie file
Genre is not X
My Rating is Greater than 3 stars
Limit to 3500 MB selected by Album
Live Updating checked
Why You Do It This Way
Smart Playlists are a little quirky about which conditions you can and can't create. For example, with a playlist that looks at all conditions, you can't designate more than one acceptable file type—if you create both "Kind is AAC audio file" and "Kind is Protected AAC audio file" conditions you'll be told that you have a conflict. You can, however, provide a list of file types you don't want it to use. This is why you see all these "Kind is not" entries for files that are likely to be large.
Had you chosen "Enable ANY of the following conditions" with all of these conditions, you'd wind up with too large a selection of songs and, likely, songs you don't need.
The other reason for sorting by file type rather than strictly by size (no files over 9MB, for example) is because such a condition is likely to cut out some of the longer selections on an album.
I've added a couple of "Genre is not" entries to my playlists so that I avoid putting things like holiday and children's music on my mini. I've also used a ratings filter to put just the songs I want on it. Using My Ratings is Greater than 3 stars, I'm able to put just the good stuff on the mini.
If you don't limit the size of the playlist (3500 MB) you could wind up creating a playlists that's too long and you're back where you started. And yes, you must enter the size in megabytes. Smart Playlists don't allow you to enter decimal values—no 3.5GB, for example.
One you've configured the playlist to your satisfaction, click OK and name it. Highlight the iPod in iTunes' Source list, and click the iPod Preferences button that appears at the bottom of the iTunes window. In the resulting iPod Preferences window enable the Automatically Update Selected Playlists Only option and check the box next to the Smart Playlist you created (uncheck any other playlists). Click OK and your mini will be updated with the songs in your smarter Smart Playlist.