What deed can I do to draw closer to Allah, other than prayer, charity, fasting, and memorizing the Qur'an?

The most important deed that brings a servant closer to his Lord is performing the obligatory duties, especially prayer, which is the first thing a servant will be held accountable for. As for supererogatory acts, prayer and remembrance (dhikr) are among the greatest means of drawing near to Allah. However, the doors of good are many and diverse, including contemplating Allah's creation, enjoining good and forbidding evil, calling to Allah, teaching people, fulfilling their needs, and supporting the oppressed. Any deed done seeking Allah's pleasure will be rewarded for its doer.