What is your background and what is the goal? If you want to learn about geometric algebra (a certain real Clifford algebra), then I recommend Alan Macdonald's books for a simple introduction that tie in linear algebra and some multivariable calc. They are *Linear and Geometric Algebra* and *Vector and Geometric Calculus*.

If you just want a short simple introduction to Clifford algebras then *An Introduction to Clifford Algebras and Spinors* by Vaz and da Rocha is good.