Many adults have an easier time learning when they understand why they are learning the subject at hand. Use real life examples to illustrate any important points. For example, if it is a math problem, you may make up an example that involves the logistics of balancing a checkbook, something most adults are familiar with.
You will get a better response out of most adult students if you involve them in some of the decision-making. For example, you can assign a project with general guidelines, and allow each student to pick his own topic. It may be a research project where you have defined how and where the work should be done, but the students are given the freedom to choose the subject. This way, they can design the project around their own interests and feel more in control. During day-to-day lessons, encourage participation, and you will be more likely to hold their attention.
Remember, education isn't a one-way street. Your adult students are likely to have life experience that can contribute to productive and informative discussions. Allow students to interact with each other in a controlled environment. They may have things to teach you or their fellow students.
Many adults are afraid to ask questions because they think they should already know the answers. To make your students feel at home, you must create a relaxed and friendly environment. Allowing them to interact with each other will help, but you should also set guidelines. Make sure everyone knows that his comments are valuable and all thoughts and ideas will be considered. Instead of moderating these discussions yourself, try assigning the task to students. This will allow them to feel more comfortable participating in the discussion.