PHP coding guidelines
The guidelines that I follow when writing my PHP scripts; can be helpful to have something like this if you're working on a joint project.
These are only the guidelines that I personally chose to follow for the code I write. This is not an indication that any other coding styles, guidelines or standards are wrong. Feel free to use this document as a template to manage your own coding guideline and change whatever you wish as you see fit.
Why are guidelines important?
First of all, let's make one point crystal clear: it doesn't matter what your guidelines are, so long as everyone understands and sticks to them. I've worked on a team where the person in charge preferred to put braces following the expression, rather than on a line all by themselves. Whilst I didn't necessarily agree with this convention, I stuck to it because it made maintaining the whole project much easier.
It cannot be emphasised enough that guidelines are only useful if they are followed. It's no use having a definitive set of coding guidelines for a joint programming project if everyone continues to write in their own style regardless. It is arguable that you can get away with different coding styles if every team member works on a different section which is encapsulated and therefore their coding style doesn't affect the other developers. Unfortunately, this only holds true until a developer leaves and someone else has to take over their role.
If you are running a joint project, you might consider putting your foot down and basically refuse to accept any code that does not conform to your published guidelines, regardless of its technical merit (or lack thereof). This may sound somewhat draconian and off-putting to developers at first, but once everyone begins to code to the guidelines you'll find it a lot easier to manage the project and you'll get more work done in the same time. It will require a lot of effort from some of your developers who don't want to abandon their coding habits, but at the end of the day different coding styles will cause more problems than they're worth.