Human factors issues
Lots of good advice above about flying the aircraft but little on the new problem of passenger care.
Once you are checked out on the 172 you will find that you will be asked to fly more passengers, leaving the loading & aircraft performance issues aside ( others above have offered advice on this ) you will be faced with people who have never flown in a light aircraft before.
You must give them a brief on how to exit the aircraft in case of emergency but this brief must not frighten them.
If you are flying during the winter you need to consider the ground you are flying over and how you and your passengers are going to survive if you end up on the ground in a remote location.
Survival preparations need to be appropriate, and these can range from a mobile phone for a flight over Sussex in the summer to very walm clothing, PLB, flares and a covered life raft for The Scotish highlands in the winter ( the life raft is a very good instant tent ).
Occasionally passengers may feel sick have a few sick bags available but don't dwel on the subject and don't let passenger illness interfere with your flying of the aircraft.
Fly the aircraft in a considerate way and avoid high angles of bank and excessive pitch movements.
Above all remember that you as commander of the aircraft are morally & leagaly responsible for the well being of your passengers from the time they step airside to the time they walk out of the operational part of the airfield.