The key is to customize your defense based on your opponents roster and GAC stats. If your opponent has a lot of defensive holds, maybe save a few more strong teams for offense. If your opponent has a really good trooper team, maybe save your NS team for offense. It can also help to think about changing up some of your squads every once in a while. Everybody sees the same teams over and over again, so trying something different will make your opponent think about it a little more and potentially make them waste a stronger team trying to clear them.
Division 1 is about efficiency so you should be saving teams that you know can get you good banner numbers for offense. Think about which teams you always see, and then figure out what’s the worst team you can use to clear those teams with good banner counts. Teams like GG and NS are typically better for defense because they always lose banners (same with DR). Teams like FO, Empire (w/ Thrawn), JTR, and JKR are all good offensive teams because they rely heavily on player control and can regenerate protection to finish with good banners.
Final tip (more specific). If you are placing you’re Darth Revan team on defense, you can usually split off either BSF or Malak to make another team stronger. Even though your sith empire will be weakened, your opponent will still have to take the same strong counter up against it to clear it.
Just a few thoughts, I hope this helps!