I generally plan out the words that I'll be hand printing on the label, even print on a sample size paper, to get the layout right. Then cut a piece of muslin 1/2" larger than sample paper. Draw lines w/ a Sharpie marker on the paper side of freezer paper, cut 1/2" smaller than muslin. These lines will show thru for guide lines so hand printing will be straight. Then iron the freezer paper to the wrong side of your muslin. Use a marker meant to write on fabric (Pigma or Zig), is what I've used. Hold muslin up to a sunny window and print your words on the muslin. You'll be able to see the lines thru the muslin to keep your words on a straight line (if that's what you want). Remove the freezer paper. When done, I always sew strips from the quilt to the outer edges of the label, turn under the edges and hand sew in place, usually in the middle or bottom right corner. I always include the title of the quilt, my name, date it was finished, my city and state, who it was made for and why. You can also add any other info. you desire.
I've also read on here to sew the label on before you do the machine quilting, so the label can't be removed easily. I have not done this however.