There are actually quite a few ways that you can increase the humidity of the air inside your home without using a humidifier. Here are some that you can try:
1. Add houseplants to your space. Plants naturally add moisture to the air through the process of transpiration. Essentially, each time you water the plant, the moisture is drawn up through the roots of the plant to the pores in the leaves, where it is then released into the room, helping to increase humidity as a result. 
2. Place a pot of water on your radiator, wood stove or floor registers. The heat will help evaporate the water into the air, which in turn will increase the humidity inside your home. 
3. Boil a pot of water. This is one of the fastest ways to raise the moisture content of the air inside your home. Simply place a pot of water on the stove and heat it up until it boils. As the steam is released into the air, it will rapidly increase the humidity of the room.
4. Hang your clothes to dry. Rather than tossing your clothes in the dryer after they are done washing, hang them on a line or rack inside your house. The moisture from the clothes will increase the humidity in the space as it evaporates. 
5. Take a hot shower. The steam from the shower should not only fill up your bathroom, but when you open the door it should also help increase the moisture in the air inside the rest of your home as well.
6. Use a Crockpot or slow cooker. Simply fill it with water and leave it turned on low throughout the day. The best thing about this is that you don't have to worry about watching it like you would if you had a pot on the stove.
This video also has some other ideas that you can try: