Would Like to add a couple of things here. Just finished this and made #1 and #2 slot on leaderboard on a few maps so I know a little about this =)
as Jorax stated its really hard to say anything about the map as each one is unique. But I can tell you my mainstay traps/spells I used and kept most of the time also some tips you may miss.
NOTE: at the start of each round in the trap section it shows what orc/troll ect are on the map at top of screen. adjust accordingly. aka you dont need an ice amulet for frost giants but its great for flyers. Anyways...
PALADINS (you will use these alot)
Lightning ring (best spell)
Brimstone. (people pass this up but its one of the best traps out there especially for kobolds)
Tar traps tar traps tar traps.........
Special note on the spells.
I did not realise this till near end of game of my first playthrough so im sure someone else missed this. but if you use the left trigger instead of right it does a massive amount of damage but also drains alot of mana so be cautious.
I always used steel weaver never once went with any other one. Always stuck to the guardian tree.
Paladins are great tanks. If you trap near them they will tank while you can cast lightning spells.
Dont use archers unless there are flyers on the Board, you can keep them safe, or the board is designed for them.They are really weak and go down to fast in nightmare mode. I used ballista instead of archers in the final few boards except stairs of doom.
Mushrooms. These are overlooked but will save your butt on a few levels. Play it by ear and see how it fits in your rotation.
Heres a link it will get you started.http://www.xblafans.com/orcs-must-die-complete-guide-27403.h...
This guy has some good tips but you will most likely have to tweak them as he relies alot on magic. Just keep the pointers in mind. Good idea maybe to watch a video before you do the board so you can get an idea of everything.
Anyways hoped this helped someone.