Tires
Pressure
Good tire pressure is essential to the performance and safety of your motorcycle. Tire pressure should be checked every few days as well as before long rides to ensure that air is not escaping. To check the tire pressure, you will need a tire pressure gauge. They can be found from anywhere between $5 and $50 typically, either from local shops or many online retailers. It is helpful to have a hose from the gauge in order to easily connect to the tire's valve stem. The front tire should have approximately 33 psi, and the rear should have approximately 36 psi. If you carry a passenger these should increased slightly.
Condition
The first thing you should do in checking condition is tread depth. Most tires have a wear bar and if it is showing then the tire needs to be replaced.
Also check for dry rot and other signs of age, such as a shiney texture to the rubber and pitting, cuts, and nicks into the tread.
Read this page for almost all the info you need to know about motorcycle tire wear.