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?
I would like to answer this question by asking one myself: would you go to a three-star Michelin restaurant, with a respectable but established clientele, with posh and smart diners, who do not need to meet their cooks or maitre's but just enjoy the glamour of the settings? Or would you prefer to visit a 1-star, striving to get a second star, where you have the occasional tourist and the owner is more keen on explaining to you the philosophy of their recipes?
I have been visiting both types (restaurants and universities!) and I prefer the second one, but it's probably due to age. In the latter you have more flexibility and contact with the main person you're interested in. Also, the first period acts as a "showcase", and it's very likely that more will be possible in the future.
My main advice would be to be a good networker. That implies "work hard" but also being prepared to "party hard", if you see what I mean. You should not be afraid to "ask people out" as much as in asking to share some research: you're likely to be in touch more often with the "second tier" (the first being the professor and her peers), and they will be the next generation of professors, so it's good to have a number of relationships with the post-docs and researchers of any institutions, at your stage of career. So don't close yourself in a shell of hard work for six months: I have seen that happening, and it does not make a good impression (to me)