I love the look of sequins and I am always on the look out for more ways to work them into my designs. As you can see by the picture my gowns for the Large and Small Baby Bratz dolls are covered with them. (Patterns on my website: http://www.donnascrochetdesigns.com/)
Sequins are fairly easy to use in crochet.
What I like to do is space them apart with a single crochet stitch. That way there is more room between the sequins so they lay better (flater) and you use less.
Normally you'll see in the instructions of one of my designs using sequins: (sc, slide, sc) across. What I mean by this is make one sc stitch, work the next stitch, but before you yo and pull through the last loop you slide the sequin down to it and then complete the stitch.
This does two things. First it anchors the sequin firmly in the stitch so it won't move freely when finished. (Don't you just hate when you have to smooth the sequins out so they all lay falt and in the same direction? I do. And this prevents it.)
Second it places the sequin to the back of your stitch. This makes working a series of sequins in easier and will less chances to catch your crochet thread on them as you work. (Another hated thing.)
After working a row of sequins I normally do a roll of half double crochet. This spaces the sequins and you don't have to worry about keeping all the sequins to one side as you work as it is done for you by doing every other row.
I've found a hdc is just about right between rows. The sequins will still look like one continous flow, but again, saving you on the number of sequins you have to use.
Give it a try! Let me know how this works for you!