Listen to Songs With the Audience in Mind
A song that sounds quite cheerful to you may suddenly not be so when you realize the lyrics are too suggestive for a twelve year old, or the guitars are too raucous for your pop loving friend. You would be surprised the different edge songs take on when you think from someone else's perspective.
Don't Feel you Have to Stick to One Genre
Maybe your friend really likes R and B. "There"s nothing wrong with putting something different on here and there. After all, many of us don't discover we like a band or genre until we hear them!
Consider a Novelty Track
Maybe you will want to have one funny track. It doesn't necessarily have to be cutesy or well known. It could be a TV theme tune or a sound effect or something else. This can also be handy if you're having trouble with the segue-way between two tracks. Throw in a random one and no one will notice!
Listen to the Whole Song
It's all too easy to put on the single mix or a live version and find it really doesn't go with the next track at all. It may also be that the track cuts in and out at odd points. You may also forget a track is actually very long!
Listen to Your Whole CD Before you Burn
Do the tracks work well with each other? It's fine to have variation, but a very slow track going into a fast one can be jarring. Consider the tempo, feeling and, if you have a good ear, key. As a general guide, if the switch from one song to the next jars then it's not working. You might also consider an on-going mood. For example, have an uplifting start, a more contemplative centre and a nostalgic end.
Cover Art
You may not have time for this, but at very least have a track listing. There's nothing more frustrating than finding you love a track, but not knowing what it's called. If you do have the creative inclination, you may find making a cover quite fun. If you're unsure you could do a montage of pictures of the bands / artists on the CD. If all else fails, you can cut out a square from some nice wrapping paper and put the track listing on the back.