Magickal jewelry should be carefully researched for content, quality and design. As far as the stones themselves are concerned, I highly recommend Scott Cunningham's Crystal, Gem and Metal Magic, Llewellyn Publications. It is a wonderful reference book, and has
just been re-released with a few new additions.
Bands (circles) are binding. They ground and bind your magick within you. Personally, I use neither rings, bracelets, necklaces nor anklets when spellworking, but I have a moonstone ring set in sterling for scrying, a charm bracelet which grants me the blessing of having situations turn out to be in my favor or for the best in the long run. These charms were all hand picked, chosen specifically for what they were and what they meant to me. Each piece is charged with the full moon, or the new moon, depending on what it's for. I have a new piece, a pentagram made with beryl, set in gold, which is charged on the new moon because it is meant to keep undesirables, users and posers away from me and mine.
You should also know that there are receiving sides and sending sides. Magickal jewelry designed to bring things to you should be worn on the receiving side, while those designed to keep things at bay, or to assist you in putting out a specific "vibe" should be worn on the sending side. The hand you use the most is your sending hand and the other is the receiving hand. Gold and other yellow metals should be worn on the receiving side only and silver and other white metals should be worn on the sending side. If you are left handed and married, I suggest a white gold or platinum band or setting over one of yellow gold; it will empower your sending abilities.
Pendants and brooches (pins) are often used and worn as AMULETS. These can be made of virtually any stone and any metal, but as with the rings, make sure you've researched and found the proper type of stone and the right accompanying metal for the setting.
The single most important step in making magickal jewelry or having magickal jewelry made for you is to properly CHARGE your piece regularly.
I wish you success in all that you do.