Know whats important to their fam and what your fams able to do.
if they have a pop banker do you have a partaxian you can jump?
IF they have a small camaar who will be annoying with retakes clear him first before war starts.
IF they have one main resourcer kill him he's probably even more important then 1 banker in their fam.
Know their savings compared to yours.
Know what systmes you can hold once you take planets/ where you need to station units and what systems of theirs you want to try and portal in that you already aren't in.
Know what your familys defense is like, make sure your bankers have enough agents to not be able to get nuked by anyone.