I agree that jewelry is personal - but I do think there are some workhorse jewelry categories that you'll be sad if you don't have.
If your ears are pierced, earrings:
At least one pair suitable for weddings and events and job interviews; these are the conservative ones like small studs, dainty hoops, or ladylike pearl dangles. Once you have these, you can have fun with the rest!
Necklace:
For wearing with collared button-downs, something that rests in the sweet spot between your collarbones and your cleavage (high or low in that area is up to you). It can be big or small or interesting or precious, but it should make you feel wonderful.
Rings:
They should be comfortable and not get in the way. For example, I have a big cocktail ring that I love, that always swings around on my hand so it's between my finger and my palm. Makes it very hard to type. Or to hold a drink. Useful cocktail ring, huh?
Bracelets:
If you type or use your hands, choose ones that don't get in the way, clink a lot (if coworkers can hear you), or hit the keyboard or table.
Very important with jewelry is not picking items that will get hooked or snagged onto knits. If your earrings, necklaces, rings etc. damage your tops when you pull it on or off, prick your hose, or get tangled in your hair (yes, it happens) it will make your day a lot less fun.
Anyway, that's what I think!