One aspect of necklace design that took me a long time to master was balance.
What I started out doing was to simply choose a lot of beads I liked and wanted to use together and start stringing them. This works fine for beads of all the same size and weight but with the beads of greatly varying weight and size that I was using, the overall result was that it would hang funny, the clasp would always end up in the front, or it just hung weird with the heavy beads making sort of a bend in the necklace.
Over time I learned that it's best to consider the weight of each bead compared to the ones next to it. Once you string a good number of beads, put small clamps on each end and then pick it up and handle it, move it to one side and the other to see how it moves.
You can even leverage the concept of weight to make large designs that are still not too heavy. This is another mistake I made when first designing necklaces: I would use so many huge, heavy beads that the finished necklace hurt my neck to wear! So to keep this from happening, what you can do is to intersperse the heaviest beads with lighter beads to make the end result weigh less. Try hollow glass beads, plastic beads, wooden beads, and pumice. Tube beads and thin, flat beads also tend to be lighter.
Make your necklaces symmetrical unless you add weight to the opposite side to account for a heavy piece. For example in my pictured rabbit necklace above, I added plenty of heavier beads to counterbalance the rabbit, while putting far fewer heavy beads on the rabbit's side.
May your creativity flow and glow!
--Pam