I suggest learning OOP before stumbling into a framework such as Zend. You will thank yourself later for it as the concepts used are for a person with little to no OOP experience quite difficult.
Once you have done that you may want to get acquainted with Design Patterns. Zend uses quite a few so its good to get an understanding on 1) What the hell they are talking about and 2) What the design pattern does.
Although I think you should knuckle down the OOP before reading about them also. Once you have got a good understanding on OOP and its principals then read Design Patterns and Zend.