Suppose you've interviewed for two post-doc positions. The first position has just been offered, but you really want to see if the second one offers a position as well. Clearly, it would be best to press the second one to make a decision sooner. But it may also be a good idea to press the first one to give as much time as possible to make a decision.
What are the most effective strategies to negotiate for more time to make a decision on the first offer? How should one phrase it in the most positive and constructive way so as to maximize the possibility of gaining more time to make a decision?