Do some research on Vapor Pressure Deficit. This will tell you what your RH should be according to temperature. I keep my room around 60%-70% RH and temps around 80-85F. The links below explains it well.
To bring your RH up you will need a humidifier or fog maker. I went through 5 humidifier in two years (spending way to much money on each humidifier) before finding the House of Hydro. You can make a humidifier with simple parts they sell. It is simple to make and easy to replace parts. It also works better then any humidifier I have bought at Home Depot or Amazon.
Here is a youtube link on how to make a humidifier with the House of Hydro parts.
I made mine similar to the one above but single disc and with a 5 gallon bucket. 5 gallon reservoir needs refilled twice a week when it is -20F outside and dry as a bone.
Cheers!
Tommy