Dos and don'ts for EFL speaking tasks

DOs:

Always make sure that the listener is required to do something with the information they are getting. 
"Tell your partner about your favourite foods" means the listener doesn't have to do anything, but "find 3 foods you both like" means that each student has to understand, analyse and evaluate what the other person has said.
If a student is presenting at the front, the rest of the class will misbehave or fail to pay attention unless they are required to make use of the information in some way such as answering questions or even making a list of "surprising things I heard".

Always make sure the task has a clear and tangible end point.
In a task like "find 3 foods you both like" the end point is when the pair has 3 items on their list which they can then show to the teacher as proof.
The best forms of proof are written or drawn in the form of lists, posters, mindmaps...anything you can show afterwards as a result of your work.

Try to make the task repetitive.
The more students get to practice the better.  The tragedy of oral presentations is that you get to do it once and for better or worse, that's it.  That's why it works better to have mingling activities.  For example "how many people did the same things you did last weekend?" means that students get to tell others about their weekend several times.

DON'Ts:

Don't interrupt to correct language mistakes that don't interfere with meaning.
There's nothing more discouraging than having every word corrected as soon as it's out of your mouth.