1. Measure your window & purchase fabric accordingly. Or, see a curtain on sale & think about how cute it would be as cafe curtains and go for it.
2. Lay fabric out flat & measure for cutting (make sure you give yourself a little extra material for hemming).
Since I used a shower curtain, with pre-cut-shower-curtain-holder holes, I just folded the striped portion of the material in half and sewed it, creating the-part-of-the-curtain-that-the-rod-goes-through. (Can you tell I don't deal with curtains a lot?) Hint: make sure you hem your sides before the top. I was not a perfectionist with these curtains (they're just in a bathroom, after all), so it only took about 45 minutes to hem. Which is still probably really long. Give me a break, I haven't made anything with a sewing machine since I was in 4-H, like 15 years ago.
6. Make the rest of your bathroom cute.