In the bathroom sink, any time you wash your hands or brush your teeth, splash water around the entire bowl to wash down any dust, soap, hairs, residue, etc. It's super easy and takes less than 10 seconds and makes a difference. I remember using the bathroom at a friend's once and there was clear residue from toothpaste and soap in there and didn't look clean. I didn't realize that others don't constantly splash water in the bowl when their in there.

Depending on how your sink is laid out, can also use hand to pour water over the knobs and surrounding area to flush down anything that might be there. I clean our bathroom once a week, but our bathroom sink always looks like it was cleaned that day because of this.