If you've never done any crochet in your life it is better to start with an easy to handle material: go to your craft store and buy a soft yet not expandable yarn - a soft cotton yarn will be perfect. While you are there, get a hook too - check on the yarn label for the hook gauge. My advice is to get a hook at least one size larger than indicate on the label, since we are using it for a different purpose than clothing-crochet. Now that you have the yarn and hook, get some beads out - their hole must be large enough to fit comfortably on the yarn. Having a few types of beads and using them in a complete random order will work best for your first try. Pick up a sufficient number of beads (count like you would simply string them for the length of necklace you want to have) and string them all randomly on the yarn.
Start a chain - check here for a Chain stitch tutorial. Crochet 6-8 stitches with yarn only.
Pick up the first bead and bring it close to the last stitch - hook a loop of yarn over the bead and draw it through. The bead should now be inside the chain stitch. Crochet one stitch with no bead. Repeat stitch with bead, simple stitch until you have the desired length. Crochet 6-8 stitches with no beads and finish the chain off.
You now have one beaded chain. There are multiple options: you can make the necklace with this strand only - in that case use the ends to finish the necklace through the desired clasp. What I enjoy more is to make multiple chains of same length (and assorted beads) and braid them together. To do that - simply crochet 2 more chains and braid all 3 together. Finish the necklace as desired.
Notes:
1. Yarn length must be 3 times the desired length of the finishing necklace + at least 5" more. Crochet is using about 3 times the length of the actual chain. Keep that in mind when you start using wire to crochet!
2. If you braid multiple chains together make the chains the finished necklace length + 5" (12 cm). Braiding will use extra length; it also depends on the size of beads: the larger the beads, the more chain is used in the braiding. There are no hard rules - experiment to find out what works best for you.3. If you start wire crochet - make sure you don't over-handle the wire. It will snap and break. That's especially true for the endings, after you braid the chains together: twist the endings together gently.
4. When braiding the chains together - don't pull too much, you want a flexible plait.
5. When making a bead chain stitch - make sure the yarn/wire is not too loose around the bead, you want the bead to stay in place.
The crochet necklace is a perfect project for any irregular beads you might have or for fancy combinations. This is truly a 'the sky is the limit' project - enjoy!
