Pick a piece and get trimming, pretty much what I did. Have a look at some of the ATA build threads, also check out those who have ATA and EIB or Centurion too .
Research is the trick make sure you have plenty of reference pictures close to you, also if there is something you aren't sure about ask, there are never any stupid questions, just silly mistakes.
One more, measure twice and cut once.
Good luck on the journey