I'd say to focus on creating wealth to get sieges. Once you do, you can think of all kinds of crazy ass traps to trap or kill the goblin invaders. It is one of my favorite things to do, personally.
Goblins, when they are near enough, will chase down and kill any tame animal outside. So all of the traps I make are based on that. I put a cage in the trap that has a tame animal in it, and hook the cage to an indoor lever. Then when a siege or ambush comes (usually siege) I'll release the animals. It is important to have the cage in some sort of room with a tightly closed door so the animals don't wander off.
From there, you can think of all kinds of awesome ways to kill your goblins. Using pressure plates and whatever else. One really simple one I build was a tower that had 2 platforms. The first one (up a few levels) had the cage and the pressure plate on it. Then up a few more levels was the other platform. The pressure plate is attached to supports. The supports are the only thing holding up the upper platform (you have to deconstruct the stairs leading to platform 2 once all the supports are linked to the plate, or it won't work.). So when the goblins chase down the caged animal, step on the pressure plate, the whole tower topples onto them, and they die horribly.
That is just one simple example, the possibilities are nearly endless.
Also make moving records of the traps as they work, they are REALLY fun to watch!