What Is The Best Way To Convert Jpeg, Bitmap, Tiff Files Etc To Vectors Using Adobe Illustrator?

I'm trying to take text or images and convert them to vectors for the purpose of graphic design using Adobe Illustrator. Text and images already created in Illustrator are in a vector format, providing it remains an AI file. If a client sends me a sample of a logo or text that he wants made into a sign 8' x 10', that exact sample has to be converted to a vector format.