Many tapestry stores offer classes in the basics of tapestry design. If you do not feel comfortable with this learning process, there are many good sources for this information. There are many books devoted to the subject.
One resource that is especially useful is the internet. There are a number of sites dedicated to the topic. These sites can give you a great deal of information in just a short period of time. If you cannot find what you are looking for at one site, you can probably find it at another. The internet is also a great way to compare prices and even place a custom order for your design.