When you have to give a gift to someone you don’t really know well and they haven’t provided any guidance, what do you choose to give that you really like?
For me it’s windchimes. I absolutely love them, so I also love to pass them along as gifts. And I suppose on the chance that my recipient ends up not liking them, I have no problem with them re-gifting them for someone else. Or returning them even.
Crystal. If they have money, it goes well with any decor. If they don’t, it’s a nice piece to bring a little class to their home. You can buy inexpensive stuff or go all the way to something expensive, and you can find such a variety of items that it’s easy to find something for people you don’t know much about.
If it is a momentous occasion, I get a silver dollar from that year. Weddings, anniversaries, graduations, they can all be remembered with a silver coin. And I usually add a check.
Flowers. Most people have plenty of stuff, and I have no taste in any case (I really don’t). So I go to a florist who knows more than me and give him a dollar amount and let him pick something pretty. High-quality florists have really amazing stuff, and if people don’t like them they can throw them away the minute after I leave and I never have to know.
Those are always a big hit with grade-school kids. Any time my kids got invited to a birthday party and didn’t know what to give, that’s what I sent, and everybody would take it right out of the box and start playing with it.
To young kids, I nearly always give chalkboards.
Adults are really hard. I would likely give some kind of food* and hope that if they didn’t like it, they could find someone who did.
*Not homemade
A bottle of wine, unless I know they don’t drink wine. Then it’s beer and/or the liquor of their choice.
For complete non-drinkers, I’m at a loss. Luckily I don’t know many of them.
I don’t have a go-to item, but I’m starting to have a go-to place. There’s a store in the local mall that’s sortof a miniature craft fair, with little displays from all sorts of area vendors who make their own stuff.
I can usually just wander around looking for something I think is cool or reminds me of the person in question, and find something I’m happy giving 95% of the time at least.
My birthday is in April. 
Something from Zingerman’s or Penzey’s has always been welcomed; we also have a local art gallery that carries utilitarian objects (measuring spoons, business card holders) that are just beautiful. They’re always appropriate, and even if the person already has a set of cocktail forks, these are something special that can be both used and displayed and suitable for men too.
A nice bottle of wine.
For females, I like to pick up a nice arty vase and overfill with flowers.
A book. If I don’t know them very well, it’s an artsy, coffee table book.
Flowers, or a gift coupon, or some delicacy that keeps well, and that most people will use eventually, like a bottle of olive oil, or a jar of chic fruit preserve.
For adults, I try to stick with consumables. I know I don’t need any more stuff, so I project that on others.
Wine (if I am under the impression the people drink alcohol); dried fruits/nuts (if I am under the impression the people eat healthier than I do); flavored olive oil; sets of flavored olive oil and vinegar to be used as salad dressing; good chocolate; hot sauce or BBQ sauce; boutique honey; boutique sodas, like root beer or birch beer or whatever; and regional food specialties or regional microbrews.
Kids get books, often crafty type things like instruction books for origami that come with origami paper. Museum gift shops are great for craft books like this.
Cigars, usually, if it’s a man. Women I like to give small carved sculptures of stone or minerals.
My birthday is in July, and I’m female!
stationary, a box of blank note cards, a nice box for display(carved wood, brass, etc)
Slinky.
It’s fun for a boy and a girl.
Is this more a function of who you know? I don’t know a single person who smokes cigars.