The most important decision regarding cage traps is whether to use them at all. They are just SO effective that many players consider their use to be tantamount to cheating. Sure, having the floor open up and spit out a cage that traps you against the ceiling is a powerful image, but . . .
1) A flimsy wooden cage is strong enough to hold and completely neutralize a fire-breathing dragon capable of ripping through doors made of solid granite.
2) That same wooden cage is strong enough to hold that same dragon forever.
3) Due to the game's (lack of) AI, 100 goblins can march down a trap-lined hallway . . . and every single one will think, "Oh, hey, the guy ahead of me, and everyone ahead of him, just got snapped up into a cage--but I should be all right. I'll just keep going."
4) Enemies lack the ability to break open cages holding their trapped allies.
If you're able to overlook these considerations, then cage traps are for YOU!
As for advice, the critical piece is to always mass forbid [d-b-f] your traps after you build them. This prevents your civilians from going out to collect the sprung cages, or to reload the traps with empty cages, while there are hostiles around. After the party's over, manually un-forbid each trap and its cage . . . and don't forget to re-forbid them before the next invasion.
Designs vary. Some people like building narrow, winding tunnels that minimize enemy archers' range advantage, others favor long, straight tunnels for maximum visibility, making it slightly easier to dislodge invaders that get "stuck" to their trapped squad leader. You might seal the exit to your trap hallway with a door, to keep out the animals that would otherwise clog up the traps that you want to save for goblins. On the other hand, trapping & killing animals can be good: Apart from the meat/leather/etc, killing an entire population group (like a wandering clan of badgers) moves that entire species closer to extinction (at least locally), so if you don't like rhesus monkeys, go ahead & trap all the rhesus monkeys.