Paint is the biggest bang for the buck. January white sales should have throws, pillows, and bedding. Study pictures to find what you like and use those for inspiration. Reach out to friends if you like someone’s style.
As Kathy suggested, start with painting, it will really change the room. Decide on décor colors, what will be the main color and what accent colors to go with your furniture. Rugs, pillows, a few knick knacks, pictures, etc. can come as you find what you want over time and that will spread out the expense also and you will be able to replace or purchase main pieces as you go. Just rearranging furniture can give a room a whole new look.
Have a design plan and set a budget. Remodeling costs can add up quickly if you are not careful. Source your supplies and gather over time as budget allows - then start your project. A fresh coat of paint can make a huge impact and is budget friendly. Go from there, change flooring, lighting, hardware, etc. See if these help you.
Start with paint and progress to decorating. What is your area or colors of interest? For decorating items like pillows, art, accent tables, decorative accents- I have been very lucky to have found some of the best items at estate sales, consignment shops and thrift stores.
For wall art in particular -Quite often to you can buy a framed piece for the glass, frame and mat and remove the art that doesnt impress you- put something new in it. Framing and moreso custom framing is very expensive.