Electrical problem
1997 Chevy Aveo 6 cyl All Wheel Drive Automatic 125,00 miles

found codes p0300 multi cylinder misfire and p0440 evap emissions system fault... what are the causes of these codes and how can they be fixed/prevented.

For the P0300 code I would suggest simply replacing your spark plugs and wires. They will wear down over time causing the engine code to come on. Nothing you can do to prevent it.

For the P0440 code, your most likely culprits are going to be a loose/damaged gas cap, vent or purge solenoid, evap canister, or fuel pressure sensor. I would start with the gas cap, ensure that it is tight and has no cracks in it.