Use cross project dependencies sparingly. They add a fair amount of complexity to your scheduling. The more links you create, the more links you have to manage.
Select a task in the successor project that occurs early in the project schedule. This way, all tasks on the successor project will get pushed out based on the earlier task, minimizing the need for multiple cross project links.
Do not hook dependencies up to summary tasks. This best practice applies to both single projects and among cross projects. The PMI highly recommends that summary tasks do not have work. They are roll ups of tasks below them. Placing dependencies on summary tasks greatly increases the likelihood that you will create circular references. Hooking up summary tasks also throws off critical path calculations. The only reason Project Insight allows dependencies to be placed on summary tasks is because Microsoft Project allows this feature and Project Insight needed to be able to import and export that information. However, it is not a best practice. (Silly MS Project!)
If you get an error or circular reference, the system will not allow you to add or edit tasks. You must stop and correct the error in logic for continuing to edit tasks.
Do not delete projects and tasks without first determining if there are any cross project dependencies. Remove any cross project dependencies, then delete the task or project.
It is recommended that you not link project A to project B and then project B back to project A. This is a circular reference waiting to happen. It will likely result in an error that could be very difficult to deconstruct.
Still want to set Cross Project Dependencies? Follow the link to keep on reading.