Mods and all that goes with it.
I spent far too many credits gearing garbage mods. I spent far too little time and resources towards getting good ones.
I wish I had farmed the rest of the Nightsisters after getting Mother Talzin when she first came to the game. I had no idea how good she was (or who she was for that matter) and only bought her pack because I saw Talia had nightsister synergy and it came with credits and ability mats as well as shards. I ran just those two for the longest time before finally smartening up and getting more Nightsisters to put with them. Heck, even then, I still used Boba Fett as the 5th for the longest time, and didn't get any others until I realised I needed them to be able to do the Ghosts of Dathomir event.
I made so many mistakes in farming, and it all boiled down to not taking a character all the way to 7 before farming someone else from the same place. Even when I did, it was too often someone I should've waited on (Cassian being my first 7* from the Squad Arena store for example).
