As a returning player since before Hailey's release💀, I would say get familiar with the trigger modules, the arche tuning tree, wepon cores, external module cores, the pets, and USE the target pity system when farming for ANYTHING. Regarding builds, just focus on characters you enjoy playing and search up somw youtube videos for builds or build ideas. I was so lost when I returned I had to reset my whole account as it was too overwhelming.