With your route planned out, and the first zombie chosen, you need to stay alive. Use your movement to juke the zombies if you can. Once those gates drop though, you need to book it. Slide on the slopes you see, and do everything in your power to get the hell away from spawn.

When you reach your first looting station, whether its a train car or a house, the first thing you should be looking for is a gun. Preferably, a shotgun or a revolver. If you spot some armor, take it, but don't risk your life for it. If you're being chased, gunjump the hell out of there and get as far away as you can, occasionally stopping to shoot the zombies to knock them back if need be.

After you've gotten your gun, you should start heading for the airdrop. If it's too dangerous to open it, or if there aren't enough people there, don't be afraid to abandon it. Being alive and having lower tier weapons is better than being dead and having none. Having a group with you to take the airdrop is a massive help.

Once you've gotten the airdrop, or decided you don't want to, you should start heading for the train. Once it starts moving, we've entered the mid game.