Note that this is a general guide only. It doesn't go into great detail, and there's plenty that it leaves out. It is intended to give a good general idea, some tips and hints, and simple suggestions regarding care of jewellery.

General Guidelines

This may seem like common sense (and it is), but you'd be surprised, so... Try to avoid doing things that are likely to harm your jewellery, or which will cause it to be exposed to dirt, heavy oils, etc. For example, take off rings and bracelets when gardening unless you protect them with gloves, remove them if you're going to be working with clay or paint, remove rings to work with electronics (for your safety as well as the care of the jewellery!), don't wear rings to work on your car or fix the plumbing, remove earrings if you are having your hair colored or chemically treated, and so forth.

Avoid exposing jewellery to strong chemicals such as bleach, ammonia, paint thinner, turpentine, petrol, motor oil, nail polish remover, industrial cleaners, etc.

Some jewellery can be tarnished or damaged by other, less noxious chemicals such as cosmetics, hair spray, perfume, etc. It's a good idea to put on these things before putting on jewellery, to avoid spraying or dusting the jewellery.

Always check for loose gems and clasps before wearing your jewelry.

Never store your jewelry in piles. Doing so can cause scratching and other damage. Instead, store them in separate sections of a jewelry box or wrap them separately in velvet, silk, or even paper.

Store beaded or "strung" jewellery flat, rather than hanging it. This will help prevent stretching.

(Well, I told you it was common sense, heh.)

Pearls

Pearls are quite delicate as jewels go. They can be damaged by by rough handling, they can be scratched if they come into contact with harder objects (such as other jewellery), and they can be damaged by chemicals (including perfume; make sure any perfume you apply is dry on your skin before you put on your pearls, or, better yet, wear the perfume only where the pearls will not be likely to come into contact with it).

Store pearl jewellery in a silk pouch, a lined jewellery box, wrapped in a soft cloth handkerchief, or in some other protective way that will keep them from coming into contact with other jewellery that may damage them. Don't store in a plastic bag, as moisture can condense inside the bag, as excessive moisture can permanently damage the lustre of pearls.

To care for pearls, wipe them gently with a soft cloth. You may use a lightly moistened cloth (plain water only!), and you should make sure that the pearls are dry before storing them. Some people recommend occasionally polishing pearls with a very light coat of olive oil (wipe all excess oil from the pearls).

Pearls should not be cleaned in a sonic jewellery cleaner, as the vibrations can cause them to crack.

One little known tip, though, is that the lustre of pearls tends to increase the more you wear them, as your body oils slowly accumulate on the surface of the pearls. This is why older pearls often have a beautiful, burnished glow.

Gemstone Jewellery

Gemstone jewellery, including lab-created gems such as cubic zirconia and moissanite, is best cleaned with water and a bit of dish-washing detergent. For a quick clean, simply swish the jewellery in the soapy water and rinse. For a deeper cleansing, get a small, soft toothbrush and gently scrub around the setting.

Most gemstone jewellery (with some exceptions; see below) can also be cleaned in an electric sonic jewellery cleaner. These devices can be purchased for a reasonable price in catalogs, jewellery stores, department stores, and online, and are very easy to use. Just put the jewellery in the cleaner with some water (and detergent if you wish) and turn it on (Be sure to read and follow the manufacturer's directions). Most sonic jewellery cleaners even come with a small brush for cleaning stubborn areas around the setting.

Some gems which should NOT be put in a sonic cleaner include: emeralds, opals, turquoise, jade, aquamarine, topaz, chrysoberyl, iolite, jasper, tourmaline, lapis lazuli, malachite, mystic topaz, rainbow quartz, and zircon (not to be confused with cubic zirconia, which is a different stone entirely and can definitely be cleaned safely in a sonic jewellery cleaner).

Some shops used to offer a solution supposedly for cleaning jewellery that was mostly ammonia; if you come across this stuff, avoid it. Not only is it not necessary, and it leaves a film on the jewels that can actually attract dust and actually make the jewels dull and cloudy.

Sterling Silver

Sterling silver jewellery can tarnish if not worn for a long time, but most silver jewellery is coated with a special non-tarnishing agent that will last for quite some time.

Store your sterling silver in an airtight, sealable plastic bag (the kind with a "zip" at the top) to greatly decrease the tarnishing. This will also keep it from being scratched by other jewellery, although silver is quite hard and doesn't scratch easily (it does scratch, though). It also protects the other jewellery from the silver!

To clean silver jewellery, you can use any commercial silver polish (just follow the manufacturer's directions). We like to use one of the inexpensive polishing cloths available at any grocery store. They're easy to use and do a great job! Be careful if you're using a paste polish, as it can be a real bother to get out small crevices.

Do NOT use one of those cleaning solutions that claims to remove tarnish with a single dip or wipe or spray. These do, indeed, remove tarnish, but they also strip the silver of the natural patina (lustre) and will cause the silver to tarnish MORE quickly and may cause it to turn a very ugly dull grey colour within a few days or weeks of "cleaning".

Stick with a good silver polish and you can't go wrong.

Gold

Gold doesn't tarnish, but it is prone to scratching. The higher the karat rating (i.e., the more gold), the softer it will be. The lower the karat rating, the more alloys are present in the metal, and so the harder it will be (but gold jewellery is never very hard, no matter how alloyed it is).

Gold doesn't require any special kind of cleaning, although a gold item set with a gemstone may need occasional cleaning with a soft toothbrush or in a sonic jewellery cleaner in order to get rid of dirt and dust that accumulates around the setting (see above).

Store gold jewellery in the box in which it came or in a lined jewellery box. Be sure to take care not to let it come into too much contact with other, harder jewellery, as this can cause scratches in the gold (normal wear causes scratches, as well, but you may as well do what you can to limit the wear and tear when you can).

Note: white gold jewellery is normally plated with rhodium. White gold should be periodically professionally re-plated as the rhodium wears, although normally this isn't something that must be done more than every ten or fifteen years.

Plated Jewellery

Generally speaking, good quality plated jewellery doesn't require any particular care that you wouldn't give to other jewellery. High quality plating is designed to last a very long time without peeling, flaking, etc. To be safe, you should store your plated jewellery the same way you would sterling silver, in an airtight plastic bag. This protects it not only from exposure to air (in the case of silver plated jewellery, this helps retard tarnishing), but also from scratches that might possibly lower the life of the plating.

Professional Cleaning and Repair

It's a good idea to have your jewellery cleaned and checked over by a professional jeweller periodically. Most reputable jewellers will do this for free (though they may limit how many items you can have cleaned at any one visit). In addition to cleaning, they can check things such as the clasps, the settings, and so forth. A weak setting or clasp is an invitation to loss, either of a stone or of the entire piece of jewellery.

Jewellers are also usually able to repair damaged plating, fix or replace clasps, restring pearls, buff gold to a high shine, resize (depending on the jewellery; some items are not candidates for resizing due to their construction), and other professional services your jewellery may require. The fees for such routine care are nominal, and can extend the life of your jewellery considerably.