Brevity. THAT is appreciated tremendously. After all, on air you'll have only limited periods of time in which to speak. If you can't be concise in your aircheck, that speaks volumes about what to expect on air.
I was a PD for many years, and here's what I suggest. PUT YOUR BEST FOOT FORWARD! The first thing out of the gate should illustrate what you do BEST. If it's a clever quip (that really is clever), a serious moment on a serious topic, communicating with a caller on the phone, being "a friend"...sounding warm and relatable, ask yourself honestly "what do I do better than most anybody else", and put THAT forward. DON'T INCLUDE WHOLE BITS unless they're very short. Otherwise move from strength to strength, and leave the PD wanting more. PDs receive STACKS of airchecks, and let's face it...in today's climate there are LOTS of great people looking for work. So make it COUNT! And MAKE IT SHORT! Smooth edits show that you're detail-oriented (to me, anyway).
As for how to get your aircheck heard, MAKE IT LOOK GREAT! Make it stand out from the crowd. Kudos to whoever is the first to send an aircheck on a USB stick that the PD gets to keep afterward! If you're sending out a CD, there's just no excuse for it not looking FABULOUS...technology like LightScribe, and LabelFlash make it a no-brainer to produce truly hot-looking discs. The trick is getting quickly into the "shortlist". You'd be amazed at how quickly a busy PD will decide whether to take your package seriously or not. MAKE IT SIZZLE visually, so he/she will WANT to listen!
Good luck!
Mike