I know this is common knowledge, but most people seem to fail to utilize it.
Skull towers have AoE damage. That means that they deal out more damage to large groups than they do to small groups (duh). So one thing you want to do, at a middle level, is to try to bunch up the enemy forces just before you bombard them. In some cases, 1 Skull + 1 Barricade can deal even more damage than 3 Skulls in a line. For example, typically a trap Skull Tower is able to unleash one volley, then dies while it’s reloading. But it always takes out one wave. Ergo, put a Lv.14 Boosted Barricade just before the trap Skull Tower… It will take a very long time for the king to beat through it, meaning that his units will be in a perfect little cluster, right when they come within range~
I hope this topic was helpful to those of you just experimenting with Skull Towers! ^.^ Remember, Skulls and boosted barricades go well together [: If you’re short on Skulls, bunch the bast**** up! =D