relax, take deep breaths, and take everything at your own pace.
Know the speeds for your aircraft, the examiner will likely ask what speed you will use for climb, cruise and decent, and want you to stick to the ones you stated.
Keep track of the navigation by writing the time on the map as you go along. Once you positively identify where you are, by a river/road crossing, or a town, jot down the time. This means you know that 5 mins later you can only be a certain distance away from this. Should stop you from panicing and mis-identifying your final destination.
If you're super relaxed, as you're going along, keep looking for an appropriate field for a PFL. If you always have one in mind, you won't be caught out when they suddenly pull the throttle lever back.
Most examiners realise you will be nervous and allow for this. Just fly safely, that's the really important thing.