@ryan @tikaro depending on where you live², IKEA duvet cover¹ are an excellent source for fabric that is cheap, easy to work with, often has nice prints, is usually 100% cotton (or at most rayon / lyocell) and is actually usable for things that will get worn (mostly tops, or very lightweight bottoms) and/or used.
And speaking of cotton, one think that will make the difference in the way your clothing will look is pressing all seams as you sew them: you don't need a fancy iron, but an iron is necessary. And cotton and other natural fibers (plus rayon) will work with you under the iron, synthetics will work against you, and will cause you lots of suffering.
¹ other than the very cheapest ones, that tend to be quite lightweight and transparent, and the fancy ones, that are probably good for everything listed above, but not cheap.
² some countries apparently have shops with cheap cotton. I don't live on one of those :D