Risk of ESD increases exponentially as humidity decreases. 40% is the recommended minimum. But, humidity is not sufficient to ensure safety.

Equipotential bonding is required (commonly "grounding", but the important bit is that all conductors are at the same electrical potential). For personnel, the bonding device MUST include a 1 MOhm series resistor.

Items which have not been in sufficient humidity for at least 48 hours are at increased risk.

Assuming your most sensitive component has a nominal ESD survivability of 250V, the maximum charge difference between items must be less than 100V.

Just crossing your legs or standing from a chair can generate very high static voltages. Removing a plastic film near exposed components is not recommended.

Charge generation happens whenever surfaces separate, including when they slide or roll.

If you want to discharge non-conducting materials, you need a balanced stream of ions, but that's beyond most home or field-service setups.