The first significant cross country after you get your PPL is a significant milestone. I have two pieces of advice.
1) If you do not have one allready get a portable GPS. Modern moving map GPS units will give you an invaluable level of situational awareness that is a great stress reducer Obviously you have to do all the regular nav planing but you would be IMO foolish to not avail yourself of all available nav aids, of which GPS is the best.
2) Weather is the biggest problem with longer flights in light aircraft. Pick a day with a stable high pressure system along your entire route. It may take a while to get ideal weather, but IMO is worth the wait. Good weather will reduce the stress and allow you to really enjoy your flight.