Apropos of nothing in particular, here are some basics for the safe use of candles.
If you're like me, and I know I am, then you've used many candles in everyday life. If you're not like me, though, candles might be strange and threatening objects used only during emergencies, birthdays, or emergency birthdays. So, here is some advice to take some of the mystery out of safe candle use.
How to set up
Many people who use candles regularly, or who are fans of Clue, have a proper candlestick in which to set up a candle. If you don't, however, there are many ways to hack up a safe candle holder out of common household items.
Use something glass, ceramic, or metal. Avoid exposed wood for obvious reasons, and never use plastic as it can melt or burn with noxious and poisonous fumes. Be careful when using glass as well; too thin or cold and the glass could shatter from the candle's heat.
In addition to proper candlesticks I have a few old teacups, saucers, and other such things I bought at my local thrift shop for 10-25 cents a piece specifically for candle use; I don't drink or eat from them. Once you stick the candle to it it's really stable.
Be sure to use clean vessels, free of dust or other contaminants which could pose a hazard. Give your dusty old candle-holder a rinse and a wipe-down before putting fire in it.
Be careful with the vessel after you've got the candle going; the vessel will most likely become hot. Keep a potholder or rag nearby if you'll have to pick it up and move it.
How to stick a candle to it? After you light the candle, tilt it horizontally with the flame an inch or two above the center of a clean, dry vessel; the flame will melt off wax from the top of the candle. Drip a few drops of melted wax onto the surface, then immediately press the bottom of the candle onto the melted wax drops. The drops will harden in seconds, and the candle will be effectively glued to the base.
As the candle continues burning, drops of melted wax will run down to the base, harden, and reinforce the whole thing. Additionally, after you've burnt one candle down all the way, you'll be left with a remaining glob of melted and re-hardened wax with a hole in the middle about the width of your candle. When you want to burn another candle you can use its flame to melt that remaining wax a bit while dripping on your new glue drops, and then easily jam the candle into that hole, and be even more stable for the next burn.
Where to set up
One of my favorite places to set up candles is one which seems really obvious to me, but takes 90% of the people I tell it to entirely by surprise: put them in your sinks. Empty kitchen and bathroom sinks are probably the perfect place to set up candles when illumination in those rooms is needed. If you put them on a tabletop, countertop, or similar there is always the possibility they might fall or get knocked over, after which they can roll anywhere and light anything on fire, with fire. However, nobody has a flammable sink. If a candle falls over in your sink, at the very worst you have a little bit of sooty wax to clean off what is, by design, one of the most easy-to-clean surfaces in your home. Just be mindful of your surroundings; some kitchen sinks are under kitchen windows with frilly curtains; take all necessary precautions to get those out of the way and minimize the draft.
If a sink is not an option and you're on a countertop or table use a trivet (those things you put a hot pot or pan on when removing them from the stove) or a square of cardboard or some junk mail wrapped in foil, to avoid scorching the surface. I have a large ceramic tile from a hardware store specifically for this purpose.
Choosing your candles
There are a few candles I'd recommend you avoid.
Tealights can be tempting due to being inexpensive, but I find they aren't worth the trouble. They are small and fiddly, they don't throw off much light, they're generally not all that safe unless you have some sort of holder made specifically for them, and the holders tend to be novelty things which aren't all that safe in practice. Changing out the old tealight can be a pain, as well.
Glass-jar candles are available in a variety of shapes, sizes, and styles, and I think they are all rubbish. While glass jars can be tempting due to their transparency or implied stability and safety, it's just not that dependable a material to put frigging fire into. I have had so many different ones spontaneously shatter on me, from cheap dollar-store ones to really expensive and supposedly high-end ones; even ones which have been blown out can explode on you from the temperature change for several minutes afterward. Additionally, the design means that the melted wax, instead of running down the sides of a candle and away, will pool up and tend to drown out your flame. It's really not worth the trouble.
Scented candles are something else I avoid. It's mostly a matter of personal preference for me, as I don't like artificial or perfumey scents in general, but it's also a matter of chemistry; candles work the way they do because of how the wax behaves, and once you start mixing perfumes and stuff into it you've got less wax and a less dependable reaction. The candle can burn faster, dirtier, smokier, and when melted the adulterated wax has a tendency to pool and drown out the flame rather than burning away cleanly. The ones with actual chunks of potpourri flakes and things stirred into the wax are just insanity, I can't see choosing to light that stuff on actual fire.
Be very wary of cheaper candles like dollar-stores might have, goodness knows what sorts of crud the wax or vessels might contain. I like saving money, but not at the expense of reliability or safety, especially when there are comparably inexpensive options which are also dependable by design; read on.
My favorite candles to have around are called shabbat candles, or sabbath candles. If you're unfamiliar; they're used in certain Jewish ceremonies, and as such usually come packaged in boxes with Jewish iconography and Hebrew writing on the box. In addition to being available in religious supply shops which stock Jewish items, many standard supermarkets will have these stashed away in the Kosher foods section. Be sure to get the cylindrical ones about 4" tall, not the taller tapered ones.
It may seem weird to use these Jewish candles for your mundane candling purposes, especially if, like me, you aren't Jewish, but they are probably the best emergency candles any household can have stashed in a cabinet. They burn brightly without being overly dangerous, and they burn cleanly and efficiently with minimal smoke. They are made to high standards due to their intended applications, which means they are made of pure, simple candle wax without cloying scent chemicals or dyes. Being shorter and thicker than your standard tapers, they're much more stable and less likely to fall over while still lasting long enough to be worth using (usually around a few hours if left to burn down all the way on their own.) One alone will serve the purpose of letting you find your way in the dark without crashing into things, and two or three around a room will light up your surroundings quite comfortably. They burn cool and slowly enough for you to hold one in your hand if you really need to, so long as you're careful with the wax drippings; you can bring one around your house to light your way. They are also incredibly inexpensive as candles go; usually around $25 for a box of 72 in my area.
If you keep a boxful of these and a lighter stashed away for a blackout, when the time comes and your neighbors are struggling to find their way around with one stinky $13 jar candle from a mall gift shop before it drowns itself in waxy perfume, you'll have enough of these babies to stay illuminated throughout the entire blackout with some left over to share if you're so inclined. Used just for emergencies, one box could keep you prepared for years. Whatever sabbath-type situations you do or don't partake in, everyone should have a box of sabbath candles handy just in case.
Safety measures for safe burning safely
Don't burn candles without adequate ventilation. A couple of these won't really affect the volume of air in an entire house, but a small unventilated room with a closed door is another story. Always have a door or window open at least a couple of inches.
Keep your candles away from open windows, air vents, or drafty doorways. A draft could knock your candle over, or cause a flare-up or a spark which is particularly bad for those who don't like everything to be on fire.
There's an invisible cone of heat rising from that flame, extending further upward and outward than you might think. Don't put candles on bookshelves or wall shelves where they might burn the wall behind or the shelf above. Don't put candles on a surface high enough where they'd burn the ceiling.
Never leave a candle unattended for any reason. If you're stepping out of the room, even for a moment, either bring the candle with you or blow it out and relight it when you get back. It may seem like a hassle, but so is a burning building. Also, sleeping = unattended. If you're getting tired, blow out the damn candle and go to bed.
Don't store your matches or lighter near a burning candle.
Keep a clear radius of at least two candle-lengths around your candle, free of anything burnable.
You may find yourself needing to disable your smoke or fire alarms in order to use candles without being alarmed; I totally don't recommend this. If you choose to do so, however, at least put up a sticky note or something reminding yourself to restore the alarms afterward.
Be very careful using candles around children or household pets, especially if said creatures are not already used to candles. Be ready to give safety lessons to kids if you have any around. During the first big blackout my family ever had, when I was very young, my mom had a great way of demonstrating the danger of a candle flame to my little sister and I; she took a long strand of hair off her head, and quickly singed it in the flame. The display was suitably intimidating that us kids stayed well clear of the candles for the duration.
Prepare for the worst. Have some sort of emergency measure in place; if at all possible have a fire extinguisher handy.