• Put your CD in a standard jewel case.   Things like slimline cases and paper and plastic sleeves don't have a large enough spine (if any at all) to make them as visible as a standard sized jewel case.   Don't go overboard in the other direction with non-standard packaging.   If your CD doesn't fit the shelf made to hold jewel cases, then it'll likely be put somewhere else - a place where it'll have less visibility.   The money you spend on packaging and postage will be worth the extra airplay you'll get.
• Mark both spines with the same information - artist name and album title are the minimum requirements.   You never know which side will face the back of the shelf,   The total identity of the CD must be readily apparent.
• Make all (important) lettering VERY easy to read.   Not all DJs have 20/20 vision.   And those who don't sometimes forget to bring their glasses.   Ergonomic studies show that red letters on a blue background don't work.   Neither do overly small or overly thin letters or letters that don't contrast enough with their background.   Liner notes on top of photos or graphics run the risk of having some letters wash out.   Avoid hand written liner notes as these tend to be illegible to everyone except the writer.
• Radio stations and DJs don't have the finances, time, or inclination to do your work for you.   CDs without cases, tray cards, or inserts may as well exclude the CD, too!  
• A numbered track listing that shows the running time of each track is required.
• A clear indication of the release's artist must be made.
• A clear indication of the release's title is equally important.   All too often, there is no way for a DJ, in the heat of the moment, to figure out which is which.   The One Sheet and Cover Letter sent with the CD isn't kept with the CD, so this information must be made clear in the liner notes.
• Your (personal and/or label) contact information must be in the cover art.   It doesn't hurt if it's on the CD itself, too.   When a caller asks how to get your disc, the DJ shouldn't have to look far or hard to find the answer.

There is no guarantee how much airplay a CD will get, if any at all.   But if you make it hard to find, hard to store, hard to carry around, hard to read, or lacking in information, you will be the reason why your CD is airplay limited or, worse, ignored.   I hope you find these tips helpful when you're preparing your CD for the real world.

Other suggested reading:   Mike Griffin's excellent advice on how to start a label or get signed to one.