Spraying with a fine mist several times a day.

Hanging wet towels in the growroom.

Open bucket of water (keep it clean though!)



High humidity is a much bigger problem. If you really want to get a grow dialed-in, it will require a large investment in lighting and climate control (digital controllers for co2, a/c, heaters, humidifiers, dehumidifiers, etc.) . If and when you decide to do this, then you can think about how to make everything optimum. But for now, if you're around 30-40% I wouldn't worry about it.