This is beneficial for you as well as your team mates. Playing on different fields will make you a better all around player. A smart thing to do is to purchase your own paintgun. That way you don't have to fool around with rental guns that your not familiar with. Before playing the game for the first time have a buddy shoot you from a distance so that you can get the first hit of the day is always the worst, after that its all down hill.
Paintballs have a shelf life of only a few months.
To increase the shelf life of paintballs try stirring them up occasionally in their container. This should help out a great deal. Also keep you paintball container sealed and stored in a cool place. They should be stored in a location where the temperature is between 55 and 75 degree. Excessive high and low temperatures will damage paintballs as well as moisture in the air.