EVAP problem and Random misfire

My car has a a few issues how do I narrow down the problem? For the last month the car has trouble going from a stop but than runs fine and it also has been getting worse gas mileage over that time. In the last few days it has been running really bad and trouble going at all. I took my car and had the codes read and it came back with EVAP problem and random misfire? What could possible be wrong or a way to narrow down the problem? When answering please remember I work on cars but do not claim to be a mechanic.