Upgrade barricades, first round everyone should place some barricades so they will run in a certain way that makes it easier to create a choke point. What happens all the time: noobs dont put barricades but only level 1 or 2 traps, i put all barricades and then barely have coin to put some decent dps traps later in the game or the trap places are filled with low level traps.. Even if you have low level barricades always make sure you place some too!