If your extension will be built under unknown or uncontrolled environments, it will be crucial to make it intelligent enough to adapt to those strange surroundings. Using the powerful scripting capabilities offered by PHP's UNIX and Windows build systems, you should be able to detect trouble and lead that unknown administrator to a solution before she needs to call for help.
Now that you've got a foundation in building up extensions from scratch and interfacing with the PHP api, you're ready to take the drudgery out of extension development by using some of the handy tools developed for PHP over the years to make prototyping new extensions quick and relatively painless.
The PHP Life Cycle
Variables from the Inside Out
Setting Up a Build Environment
Your First Extension
Working with Arrays and HashTables
The Resource Data Type
Startup, Shutdown, and a Few Points in Between
Diverting the Stream
Configuration and Linking
Setting Up a Host Environment
Appendix A. A Zend API Reference
Appendix B. PHPAPI
Appendix C. Extending and Embedding Cookbook
Appendix D. Additional Resources