1. Our first priority is to maximize contrast between our background and our text. Having text that looks great is slightly less important than having text your audience can clearly read. I generally prefer to stick with white letters on darker backgrounds, instead of off-white or yellow.
2. Shadow and outline your text. Doing this will help to clearly separate the text from the background, and will cause the text to "jump out". You can often get away with using a lighter colored background when you are using this technique.
3. When choosing fonts, remember clarity is king. Many fonts are interesting to look at but very hard to read on a projection screen. In particular, some of the more ornate script fonts tend to be unusable for projection. Thick block letter fonts such as Tahoma, Arial, Verdana, and Franklin Gothic are safe and very readable. Most projected fonts will also look better in bold.
4. Experiment with using a variety of readable fonts. While I would always suggest staying with the same font for an entire song, mixing them as we move from song to song is perfectly acceptable and can add creative interest. For instance, we generally recommend script or brush fonts for slower, more worshipful songs, and more contemporary-looking fonts for faster praise songs. You also will want to coordinate your font choice with your background choice - they should always blend nicely together and reflect the tempo and tone of the song.
For projected sermon notes, if there is a particular readable font to goes well with the theme and background, feel free to experiment with it. Otherwise, sticking with one of the "safe" fonts is perfectly acceptable.
Push yourself creatively in the area of font choices. It may seem inconsequential, but picking the right font can help add to the cohesiveness of your communication.