The most common and recommended is blue background with yellow text, its the most readable.
Use Tahoma or Aerial font.
A serif font such as times new roman can be used for titles, its harder to read and makes the audience slow down a bit
Set your laptop in front of you and the screen behind you. Avoid or never turn your back to look at the screen. I use a remote control pointer and I can see the arrow on the laptop screen and can read off of the laptop if required
be consistant on your slides and design them for user ease.
Example I put a small year perhaps 18 point font in the upper right hand corner to indicate when a state code rule was adopted.