The professional room treatments were a little too expensive for me, and the science of treating a room just goes over my head, so I improvised and made some moving blanket baffles. They are very easy to make and easy to assemble and disassemble so you can put them away when you are done recording or have visitors over, won't mark the walls and you can take them with you when you move.
In addition to the baffles, I had tall bookshelves covering one full wall. I pulled random books "out of alignment" to make the surface uneven, the way they do with those expensive wooden sound diffusers. I also tacked old pillows into the upper corners of the room and stacked the family sleeping bags in one corner.
It's not high tech, nor pretty, and I didn't get every area, but it helped reduce the sound reflections a lot and made my recordings sound much better.