Explain to everyone they are probably familiar with fractions in one way or another. If they used a percentage or said three-quarters when describing a piece of pie, then they have used a fraction before.
Draw a vertical rectangle and draw a horizontal line through the middle. Ask if this were a glass how full would it be? The class response should be "half full." Explain everything you are doing as you are doing it, to cater to auditory learners.
Write 1/2 next to the rectangle and describe what the numbers mean. The one is how much is full, or how much is being used, while the two is the number of total spaces available in the whole.
Explain the numerator. This is the top number and will pertain to the number being discussed or that is operative. This will be the number that relates to being "full" or "used." Describe that if the full pie were composed of 10 pieces, but there are only six pieces left, then the numerator would be six.
Explain the denominator. This is the bottom number and describes the total number available to make the whole. Describe that if the full pie were to be composed of 10 pieces, even though there are only six left, that the denominator is still 10.
Relate fractions to money. Many adults understand money and can relate it to fractions. A quarter is just that, one quarter or 1/4. Use this to show how 25/100 is reduced to 1/4 and how 1/4 makes sense to describe the coin.
Relate fractions to percentages. Explain that all percentages are a fraction out of 100. You can also use this to show how 25 percent is a quarter is 1/4. Once you have related the fractions to enough tangible examples it will become easier to grasp.