Replace the Fluids and Filters
One way to start up that old engine is to make sure the fuel, oil and engine coolant are all flowing properly. We already talked about lubricating the engine before you turn it over, but another major factor that causes old engines not to start is old gas.
Gas is a highly refined product that vaporizes and combusts easily. The same chemicals that give gas these properties are also the ones that allow it to evaporate over time and cause the gas to lose its ability to ignite easily. In addition to evaporation, a process called oxidation can occur, when chemicals in the gas mix with oxygen. This produces deposits in the gas that can clog fuel lines, fuel filters, the carburetor and fuel injectors. Gasoline that has ethanol in it also tends to draw moisture out of the air and can contaminate the gas as well.
To start an engine that has old gas in it, you may need to pump fresh gas into the system from an external source. You may also need to completely remove the old gas from the tank and fuel lines before trying to start the engine.
In addition to replacing the old gas, the antifreeze will likely need to be replaced as well. Antifreeze breaks down over time and forms acids that can hurt your engine. Some people recommend using water, instead of coolant, when you're first starting the engine. If there's a problem with your head gasket, you don't want antifreeze (or water) leaking into the cylinders.
If your coolant and the gas are good you may still need to replace the fuel filter and oil filter to get the engine started, or at least to keep it running. The old filters will likely be clogged and they'll keep you from getting oil and gas to your engine.
If changing the gas, coolant and the filters doesn't work for your engine, you may need to try a different approach.