If someone cannot attend Selichot at midnight due to work or other obligations, what is the minimum they should try to do during the aseret yemei teshuvah, the ten days of repentance?

Selichot is a custom, not an obligation; missing it for commitments is permissible. During Aseret Yemei Teshuva, prepare for Yom Kippur by committing to real change. This entails daily cheshbon hanefesh (self-accounting for wrongs before sleep) and dedicating a fixed, uninterrupted hour to Torah study (increasing if you do less). Also, increase other mitzvot like tzedakah. The goal is transformation: fix middot, deepen Yirat Shamayim, stop sinning, and make a genuine commitment to lasting change. Without this commitment to cease sinning, Yom Kippur's atonement is futile.