How to make an unfinished basement a little cozier? : diy
First of all, control moisture. Tape a clear sheet of plastics, about a sq ft, to the floor. Tape up all 4 sides so it's completely sealed. Check it again after a day or two. If you have moisture, then find a way to control it. Check the walls. Is it damp? If the house is fairly new (no older than 10-20 years), then it's most likely moisture in the air condensing on the cooler wall. But if the water is at the bottom of the wall, it could be water leaking in. You have two options: if the basement is conditioned, then air conditioner during summer will take care of the extra humidity. During winter, heated air will actually dry the air so a bit of extra moisture coming in won't be noticed. But if the space is not conditioned, consider getting a dehumidifier. Depending on how large the basement is, it might be a bit noisy.
Another low-tech option is to run a pipe with an inline fan vertically up and through a window. Bottom of the pipe should be about an inch from the floor, and it should vent outside. You will be amazed at how well it sucks out damp air. Doesn't work as well as a dehumidifier, but it should be quieter.
Once you have moisture under control, do the floors. Rugs are nice but it can get expensive. See if you can pick up carpet remnants for cheap. Make sure the get underlayment. Carpet by itself on concrete is not much better than bare floor. Glue it directly to the carpet using some spray adhesive. See if you can get some interlocking foam activity tiles. I got mine from Sam's Warehouse for my kids. One side has various colors, but the other side is basic dark gray. It's pretty durable and very nice to walk on.
Walls and ceilings are more about your taste. YOu can find things to hang or cover and they will make the area feel more cozy and dampen the echo effect.