When tower positions can be paired together, use them to your advantage in a blockade. Position an archer tower across from a melee tower to allow the archer tower to help eliminate the enemies that are busy with soldiers from the melee tower. Use that type of positioning to deal with the long lines of enemies that appear in waves. With your melee units in heavy armor and powerful area of effect arrows for your archer towers, you can eliminate that type of threat easily. Place hero in your last blockade to mop up the survivors. For example, the mage casting his fireballs. Certain will move down the lanes in packs, which can overwhelm your defenses. To avoid this, thin out the pack early. When a steady line of monsters is moving down a lane, use a special ability in the middle of them to break up the large wave into two smaller waves. This will allow your tower blockades to have a better chance at taking them out. Focus on having archer towers for the first part of the game. When upgraded, they are deadly against your enemies. Upgrade the towers in the last portion of the lanes first. This will help guarantee any weakened enemies will not make to the end.