Originally this was just supposed to be a quick once-over-the-stencil with the spray can while the dog played in the yard, but turned into a full-repaint (which the bike needed anyway).
The technique here is *far* from looking "nice", but for the "rattle can black" aesthetic that I think fits this bike, it's perfect.
(If you really want a nice, shiny looking paintjob, you should absolutely sand down the old paint first, prime the frame, wetsand between coats, and then apply a clear coat.
Panda Face has an instructable for that here: https://www.instructables.com/id/Bike-Painting-Tips/)
Here are some things you'll want for this:
1: Paint (obviously)
2: Metric Allen Wrenches
3: Big-Huge crescent wrench
4: Lots of painters tape
5: 15mm box wrench
Step 1: Take Off the Wheels and the Seat
Turn the bike upside down and let it rest on the handlebars and the seat.
The front wheel is a "quick release" and can be taken off with finger tools, the rear wheel requires a 15mm box wrench (or socket).
To get the front wheel off, actuate the quick release lever, loosen it a few turns, and the wheel should just lift out of the fork. (If this bike has wide tires, you might have to also disconnect the brake. To do that, manually pinch the brake together with your hand, and lift the cable out of the retainer on the brake. When you do this, the brake will be allowed to fully open, freeing the wheel).
To get the rear wheel off, you'll need to loosen the 15mm nut on both sides. The wheel should then lift out. My bike doesn't have a rear brake, but if yours does, use the same procedure from the front brake. If it has a *coaster* brake (meaning you pedal backwards to stop), you'll also have to remove a 4-5cm long "brake arm", which is attached to the frame.
For the seat, there is a bolt that you'll loosen near the back of the seatpost, which will free it. Just loosen the bolt, and pull the seat out. Your seat may also be fitted with a quick-release. In which case, just actuate the lever, loosen it a couple of turns, and pull the seat out. If the seatpost is stubborn, rotate it in the tube a few times, which should loosen it up.
Step 2: Take Off the Handlebars
Taking off the handlebars is really easy. Loosen this allen bolt, (don't take it out, just loosen it) and the handlebars and stem will lift right out of the front forks.
Step 3: Take Out the Front Forks
Beneath the nut is a washer, and below that is something called a "race". It rotates against the top set of ball bearings. The race should just come off with your hands, but if it doesn't you can use a rag for extra grip. If /that/ doesn't work, you might need to get a vice grips or wide-mouthed-pliars. Really, though, as you'll see during re-assembly, this shouldn't be tight.
Once these three things are removed (nut, washer, and race), the fork will fall out of the frame. At the top and bottom of the tube that it fits in are some cups, and in those are some bearings. Do not lose the bearings.
Step 4: Cover Everything With Tape.
Everything on your bike will be either covered with tape, or covered with paint. Choose wisely.
(In seriousness, though, cover the wheel dropouts, the front-tube where the fork fits, and if you're me and missing some parts, the cranks, and the chain.)
(In the picture you can also see my hideous, improvised-out-of-rope bike stand. Ugly-as-sin, but it worked.)
Step 5: Paint It!
The effect is *very* low-contrast and subtle, and looks really nice.
At this point, spray down the bike and the fork with your paint. (Again, this is more about disassembly that proper painting techniques. Check here: https://www.instructables.com/id/Bike-Painting-Tips/ for a good walkthrough of proper painting)
Step 6: Wait for the Paint to Dry!
Beers and bicycles tend to go together quite well, so have some friends over, work on your zombie-apocalypse plans, ponder your place in the Universe, or do like I did, and give the dog a bath.
Step 7: Reassembly!
The race (the flatish piece that sits against the ball bearings) threads on first. This should really only be finger tight. You want it right at the sweet spot between "my fork is rattling around in the frame" and "I can't turn my fork". The fork should spin freely, but shouldn't rattle around.
This takes a bit of finesse, and you probably won't get it right the first time. Tighten it down with your hand until the fork spins freely, but doesn't "jiggle" in its housing.
In the first picture, you can see the race sitting on top of the bearings. This holds the fork down. Again, this doesn't get tightened very much, just use your hands for it.
In the second picture, you can see the washer. Notice the tiny little tab at about 11:30 on it. That tab fits into a slot in the threads on the fork. Look at the threads on your fork. Do you see that notch that goes vertically through all of them? Line that notch and this tab up with one another :).
The thing that *does* get tightened here is the locknut. This is the 30mm nut that you took off with a gigantic-crescent-wrench in step 3. What you're doing is holding the race in place. You're just tightening the nut against the race here. Make it tight, but be careful not to strip it. Also keep in mind that some of the pressure you apply here will get translated through the race and into the bearings. If your fork doesn't rotate freely after tightening this, loosen the locknut, and then loosen the race a few degrees. Like I said, it takes a bit of finesse.
Also keep in mind that you now know how to service this part, so if it becomes loose, you can just tighten it. I'd rather re-tighten a nut like this than end up stripping something. Use your best judgement.
The other things (stem/handlebars, wheels, etc.) are simply the reverse of what you saw in steps one and two. If you have a fixed gear (like this), here is a trick for the rear wheel:
Tighten the drive-side nut first. This way you can properly-tension your chain (think like a guitar string. It should move a tiny, tiny bit, but shouldn't be flapping around), *then* worry about straightening the wheel.
And that's it! Take your bike for a quick test-ride around the block, and be sure to pay attention to if anything feels loose. The nuts holding the rear wheel on should be fairly tight (although gravity is mostly what is holding this in place), as should the nuts on the front wheel. Pay double attention to your fork. Does it feel like it's jiggling around in the frame? You need to tighten the race a little.
Now go strut your cool new paint job :-D