When using visual aids there are a number of important rules to be followed which are listed below.
DON'T look at the visual aids: look at your audience. As an example you may be writing on a whiteboard. It is very tempting to talk at the same time to avoid the dreaded "silence" during your speech/lesson. Complete silence is actually better than talking with your back to the audience as that is considered to be rude.
KEEP visual aids out of sight until you need them. leaving a model forklift truck on the desk whilst you talk about something else is almost guaranteed to have someone picking it up and getting distracted by it.
BLOCK CAPITALS are the best when writing on a flip chart of a whiteboard unless your handwriting is very neat.
LETTER SIZE: Can your great visual aids actually been read by persons at the back? If in doubt, check it out as part of your preparation
PRACTICE. It might sound a funny thing to say but you should practice actually using visual aids so that it becomes natural and doesn't distract the audience.
One of the funniest things I ever saw was during an instructor course I was conducting in Saudi Arabia when the excellent visual aid that the trainee had made collapsed in a heap when he tried to use it. It cause a lot of laughter amongst the rest of us but he couldn't continue with his lesson on forklift stability.