If you are just starting out designing type, I just picked up this great book called Designing Type by Karen Cheng. It explains the processes behind creating and designing type and provides detailed guidelines for creating serif and sans serif letters, numbers, punctuation, and accents.

"The book is illustrated with numerous diagrams that demonstrate visual principles and letter construction, ranging from informal progress sketches to final type designs and diagrams. A wide range of classic and modern typefaces is analyzed, including those from many premier contemporary type foundaries. Introductory essays and diagrams emphasize the history of type, the primary systems of typeface classification, the two main proportional systems for type, the parts of a letter, the effects of new technology on design methodology, the optical illusions that affect density and balance in letterforms, and the differences in form between basic serif typestyles."