Use varying sized Throw pillows. The best way to create a comfortable sofa that you can dive into is by layering your Throw pillows. This adds dimension, and texture. I like to use a 20x20 as my base, then an 18x18, and a 12x20. I often use three pillows on one side and 2 pillows on the other, I then balance the corners of my sofa with the color pallet.
Use the style in 3's rule. When choosing your throw pillows consider using a solid color, a textured pillow, and a patterned or floral printed pillow. This creates flow from end to end of your sofa.
Use colors that compliment eachother but don't necessarily match! Mismatched Throw pillows are all the trend, and can be a challenge. Here's my advice, if the colors compliment each other, it will look timeless. Don't use all neutral pillows and then one fluorescent pink one. How do you pick which colors to use in your pillow set? Take inspiration from your art! Pull colors from your art work and encorporate those colors into your throw pillow arrangement. This will balance your space, keep your guests eyes moving around your room, and allow them to take in your space as a whole.