Solomon's Knot stitch (also known as Lover's Knot stitch) is a decorative, lacy crochet stitch that would be ideal for a scarf. This video shows one way to create the Solomon's Knot stitch.
Sewing in your yarn tails when you've finished crocheting can be tedious, but doing it properly makes for a much more polished look in your finished item. Teresa from The Art of Crochet shows how to do this successfully.
This video shows how to make a scalloped crochet border. This border would work well on both knitted and crocheted items. The only stitches you need to know to make a scalloped border are single crochet, double crochet, and chain stitch.