Sometimes fastening off your work with a slip knot can look awkward. Here is an alternate method that you should use to avoid that ugly little knot ruining your beautiful work! I didn't invent it, but this is how *I* do it.
Step 1: In this photo the last stitch I made was a HDC (you could use this for SC or DC also). Instead of finishing this piece with a SL ST, I just clipped my yarn & pulled it through the HDC. Leave a good 6-8 inch tail for weaving in the ends.
Step 2: Take your needle & thread it under both loops of the first stitch of that round. (as shown)
Step 4: Weave the tail of the yarn SECURELY into the wrong side of the work. Look at the right side... No ugly knot. :)