Planning is key. Start by sitting thru IM, IM2 and TIH and working out the timing issues - when things happen, how long they take and where events overlap and reference the other films.

Lay them out in a spreadsheet with each film on a different row in a different color, with the columns breaking up individual scenes and sequences. That will allow you to shift things around and adjust how the elements need to align and interact. The more of these problems you can solve "on paper", the easier the real edit will go later.