How do I balance perfective/imperfective verbs in 20 minutes a day?

As a busy professional, I only have about 20 minutes of dedicated study time each day. I’m currently stuck on the aspect of Serbian verbs—understanding when to use the perfective versus the imperfective aspect is taking way longer than I anticipated. Does anyone have a system for 'micro-learning' these grammar points without getting bogged down in theory, or should I just focus on memorizing phrases instead?