Wooden spikes are virtually useless, and ARE useless if the target has armor - replace them with metal ones ASAP. Additionally, you do have your cage traps after the weapon traps, right?
(Besides that, these are just suggestions and not something you need to worry about right now. You can easily do it without complex constructions and math to calculate fields of fire and stuff like that, but if you go through the effort for a fort you plan to have for a long time, it makes defense easymode. However, I'd say, ignore most of the below for now unless you read a part of it and go "Oh, that would be an easy change, that's nice".)
Stonefall traps are nice, except for the reloading part. If you have the extra materials, it is far better to use more weapon traps instead. With that in mind, it's best to have several extra layers of stonefall traps if you do use them. Weapon traps --> stonefall traps --> cage traps. One advantage of stonefall traps is that you can do it all with rock - you need to spend no metal, and so (because rock is quite plentiful, natch) can be deployed in very, very large numbers.
If you're feeling creative, you can create a long, winding (single tile wide) side passage lined with traps as the main passage is sealed off by a drawbridge. one end of the passage is before and one is after the drawbridge.
If you're feeling malicious, you can have the area around your winding passage dug out, with a long, long drop (20z ensures 100% death rate) ensuring they stay on the path. Or, they dodge the weapon traps off the edge and have a long fall.
You get bonus points if there is magma at the bottom. You get double bonus points if you can drain the magma pit to collect the
goblinite for melting.
Of course, because you didn't plan for it from the beging you may not have space for such an elaborate setup. With your next fortress, keep defense in mind as you start - usually it means making the entrance hall some 25z long before you start branching off, which slows down initial hauling inside quite a bit but is worth it for the increased defensibility sometimes, depending on the map and how urgent moving inside is. An alternate option is to seal off the first entrance after you complete a second, more defendable one.
If you have a canyon, long bridges give your marksdwarves good target practice for any crossing nasties.
Something people neglect sometimes is fields of fire - if you go that far (and you will likely need to in a really advanced fortress that will last several in-game decades), make sure there are no blind spots where your dwarves cannot shoot something in the area of the entrance.
Besides, elaborate defensive constructions are something to use all the stone you're going to get for. And remember, this is just my take on it - in the end do what works for you, not what someone else tells you to do.