If you are alone with at turret and healthy enough, move forward of the turret just slightly to tank the incoming mininon wave so the incoming minions will target you and not your minions. Focus on killing the enemy minion wave letting your minions target the turret and die to the turret denying CS to the enemy team. Once the enemy minion wave is dead then you can focus down the turret with your minions.

If your health is somewhat low you have a decision to make. Can you clear out the enemy minion wave fast? If so then nuke the minion wave and leave. This will give your minions maximum uptime on the turret and give you the greatest margin of safety.

If your wave clear is **** and your health is low, then just leave.

Also if you can push in an inner turret before 15 minutes. They have no armor.