Team development
One of the features we are missing the most in the APEX IDE versions, until now, is a built-in support to facilitate a multi-developer environment. That's going to be changed in APEX 4.0, but for now, it's important to be familiar with what APEX does give us.
Lock your pages
The lock pages feature is a much underutilized feature of APEX and should always be used when there are multiple developers working on the same application. The lock pages feature enables developers to place a lock on a specific page that they are going to work on, which prevents other developers from modifying it. The other developers will still be able to view and run the page, but are not able to make modifications. This prevents developers from changing the same code and interfering with each other. The Lock Pages feature can be accessed by clicking the padlock icon
for unlocked pages, or 
for the locked ones. It's the third icon from the right on the Action Bar of the Page Definition...
