Illustrations are great for giving your information a unique look. You can also be in charge of what they look like, and you might be able to show things that would be very hard to photograph.
Getting illustrations done means finding a budding artist you know, or paying someone like an illustrator or artist. Here's some things to think about before you commission an illustrator to do some drawings for you:
Find an illustrator who's work you like. Check out a few different people's work if you like.
Make sure everyone at your end likes the illustrator - you're paying, so pick someone you feel you can work well with.
Let them know what you want to do with the artwork... make a booklet? Use in a video? Put on your website?
Tell them who the audience for the illustrations is.
It's probably a good idea to work out the words before you get illustrations done. Show them the words, and what you need pictures to go with.
How soon do you need the illustrations, and how do you need them - on paper, or on disk maybe?
Work out your budget, and be clear about how much you will pay for the illustrations.
Talk with them, and ask questions if you're not sure about anything. The more clearly you can articulate your needs, the closer they'll be met.