PC and monster weaknesses are very easy to look up and apply, but finding out what the actual people at the table will fall for is a lot harder, so what have you noticed your players always get pulled in by?
My normal process is to plan a session and then have it almost immediately derailed through a mixture of distractions, roleplay (or skipped roleplay), and sequence breaking. The planning done for a single session generally correlates to either 1/2 of a session or 2-3 sessions of useful content....