Many PhD programs envisage for every candidate a period (3, 6 months or more) in another university, in order to carry on research in another institution, acquire new skills and (maybe) lay the foundations for a postdoctoral fellowship.
The task could be useful, but involves some problems, too. Often the PhD student is not able to familiarize with the new scientific environment and start working efficiently with the new group. Also, it is often difficult to find a research group that suites one's scientific fields and projects.
More over, sometimes the supervisor from the hosting institution agrees in welcoming a PhD student from outside (also to get his/her lab more international), but he/she has no time to dedicate to him/her...
For all these reasons, and more, sometimes a period abroad for a PhD could be very useless and ineffectual.
What do you think makes a period abroad successful?
Do you have any advice for PhD students going to face this career phase?