Good tip is, if you can't answer, get the POH and tell him from that;
Actually, not so much a good tip as a vital requirement. The examiner will want to know you know how to use the POH. So he will continue to drill down on you with ever more complicated questions you can't possibly know, until you break out the POH.
When I did my flight training another candidate actually got a partial fail for not knowing where to look up basic things in the POH. Oops.
What helps a lot is to know that most, if not all, POHs of certified aircraft have a certain order in them. That makes it rather easy to look things up even if the aircraft is unfamiliar. If possible, grab a few POHs from different aircraft (internet-downloadable copies will work just fine) and compare the table of contents.
Of course, there are certain things you have to know, instead of having to look it up. A rough idea on how far and how long you can go on full tanks, and how many bodies you can carry in that case. MTOW+ISA+nil wind landing and take-off distances, a couple V-speeds and so forth.