Duel is not a very complex map as indicated by the name. You will see it snakes through the middle with the only neutral creeps being in the middle section. This allows you to secure your entire side before anything serious happens. When you are ready to move out, it is time tostart destroying those neutral forces.
There are a few things to be wary of. We should start with the back door. We all know what the back door is. When someone drops a powerful unit on your doorstep from behind. This allows that unit to do a lot of damage. There are no power pads in the back of your base and it is on a separate pathway that can easily keep a tank alive for 15-20 seconds. That is enough to lose the game.
Another serious spot to watch for is your farthest back outpost. The reason for this is that enemy creeps will come down the two far sides. This means if it is left undefended it will most assuredly be captured. Even without the other player trying. Let alone if he did.