How to easily install rear disk brake wheel without service stand

The easiest method for me is to flip the bike upside down and install it that way, so you can see the gears and brake alignment and verify that they're correct. Standing beside it, grab a fork leg with one hand and the seat tube with the other, and flip the bike. Pick a soft surface of course so you don’t scratch your bike.

From there, pull back on the rear derailleur to give the chain enough slack for you to slip the wheel in. Check that the chain is on the cassette and that the rotor is between the pads, not between a pad and piston or something. There you go!

If you have QR axles, I like to lightly fasten the wheel, then flip the bike right side up again so I can properly press the wheel into the dropouts before fully tightening the skewer. With through axles, you can screw them in with the bike upside down, no problem.

There isn't a trick - there are lots of little techniques people might use, or don't by personal preference.

Start by putting the shifter into the highest/hardest gear, which is the chain on the smallest tooth-count sprocket.

Personally I keep the bike upright - my only disk-brake bike can't go upside down because its a recumbent.

Then I have the rear wheel to hand, leaning against my right leg while I stand on the left of the bike, facing rear/right across the dropouts.

I lift the rear of the bike using two hands, and then use my right hand to grab the wheel and feed it between the stays. I juggle around and use the right hand to "extend" the rear derailleur to allow the cassette to slip into the chain. Often the bike will rest the underside of the stays on the QR. That's OK.

I then simply jiggle the bike about until the rotor goes between the caliper and the dropouts fall onto the axle-stubs. This sometimes goes really easily and sometimes takes 20 seconds of faffing.

Then I make sure the bike's weight is on the axle so its seated, and do up the QR properly, so the lever ends up upward and not touching the frame.

Final checks, I lift the rear of the bike and spin the wheel by hand. I'm looking for frame rub and maybe brake rub, and anything that is just wrong. Also test that the brake on this wheel works right and retracts when released.

Note that you'll be starting in your hardest gear, so consider changing gear while stopped before pulling into traffic.

Some people put wheels in with the bike on its side - I can't do this at all; it just doesn't work for me.

Even after numerous times doing it, sometimes it is just as hard as the first time. A few hints that may be relevant.

1. As other answers suggest, before taking the wheel off, shift the chain on the smallest rear cassette's cog. That has numerous advantages before any other position: smaller chain tension to struggle against, you know for sure where the chain should go.

2. If your rear derailleur has clutch mechanism, disengage it before the installation, and re-engage it after your are done. Again, the smaller chain tension to fight against, the easier it goes.

3. Actually take the chain off the front chainring and let it hang loosely on the crank or chainstay. That is to addition to the first two measures to make sure the chain is as slack as possible. It is easy to put it on the front cogs once the backend is done.

4. If you have hydraulic brakes, use a pad spreader tool to spread the pads. This will simplify with zeroing in the disc between them. After you are done, press the lever a few times to reposition the pads to their previous position.

5. Actually hang your bike by the saddle on something. It does not have to be a stand. It can be a branch tree, a fence, any non-sharp angle that is sturdy enough and not too high/low. This way, you won't have to wrestle with the frame's weight and focus on the fine-manipulating the wheel. This way you wont' have to flip your bike upside down and risk scratching the saddle.

Finally, re-check that your rear dropouts are not bent. If bent, it could make inserting the hub quite hard.