Here's a good 2 part series called Develop rock-solid code in PHP: Use variables effectively.

Part-1[ http://www-106.ibm.com/developerworks/library/wa-phprock1/?t=gr,phb01=PHBvariables1 ] provides good information about factors that must be considered during planning, designing, and even writing code.

The second artice[ http://www-106.ibm.com/developerworks/web/library/wa-phprock2/?t=gr,phb01=PHBvariables2 ], just released, shows you how to use variables effectively. It also shows how to make script configuration easy by constructing a configuration file parser using variable variable names in PHP.