There are many sims where the landing point is obviously misconfigured. This led me to believe that not exactly few users don't know how the landing point configuration works.
So let me try to explain how to configure it.
In Firestorm, click on "World" on the menu bar in the top left, then on "Parcel Details". Alternatively, right-click on bare ground so that the circle menu opens, then click on "About Land..." Either way, you'll get the window which the picture above shows.
The landing controls are at the bottom right; I've drawn frames around them.
Before I explain them, there's another important thing to know: There are two ways of landing on a sim or a parcel. One is without coordinates. Copied hop addresses from OpenSimWorld are always without coordinates. And if you use the map to search for a sim, and you just click the sim mane, it's without coordinates, too.
The other one is with coordinates that define where the avatar should land. Landmarks are always with coordinates. Many sim-to-sim teleport scripts use coordinates. Hop addresses can contain coordinates. And if you use the map, and you click on a certain place on a sim, it's with coordinates, too.
Now to the actual controls:
The buttons in the blue frame are for the landing point. If one is defined, you see its coordinates above the buttons and the orientation angle. The menu in the red frame defines where avatars land; I'll get to that.
If no landing point is defined, avatars that come in with their own coordinates (e.g. by landmark) will land at these coordinates, and avatars that come in without their own coordinates (e.g. through OpenSimWorld) will land at 128, 128, x.
In order to define a landing point, go to where you want the landing point to be, turn into the desired direction, and click "Set". The landing point will be defined as where your avatar is plus how it's oriented.
"Clear" deletes the landing point setting. "Teleport" takes your avatar to the defined landing point.
The menu in the red frame under "Teleport Routing" defines where avatars land when they teleport in.
"Blocked" means that avatars cannot teleport onto this land at all. They may still walk in or fly in (if flying is allowed) or come by boat or train or bus or whatever, but they cannot teleport in. Careful: If used on an entire sim, "Blocked" renders landmarks and OpenSimWorld hop addresses useless because teleporting onto the sim is not possible at all.
"Landing Point" means that avatars are forced to always land at the landing point. This setting mercilessly overrides their own coordinates. Coordinates in landmarks become null and void. Even if avatars have carefully chosen a nice place to land, e.g. at a bus stop or on a wooden pier or something, and taken their landmark there, they won't land there; they will be forced to land at your landing point.
"Anywhere" means that avatars that come in without their own landing coordinates land at the landing point. This setting prevents them from landing at 128, 128, x. It does not override an avatar's own coordinates. So if avatars want to land in a particular place on the land, they can do so.
tl;dr: Where do avatars land?
No landing point defined:
Via OSW beacon: 128, 128, x
Via hop address without coordinates: 128, 128, x
Via hop address with coordinates: Coordinates at the end of the hop address
Via map, no place on the land selected: 128, 128, x
Via map, particular place on the land selected: Selected place
Via landmark: Landmark coordinates
"Blocked":
Via OSW beacon: No teleport allowed
Via hop address without coordinates: No teleport allowed
Via hop address with coordinates: No teleport allowed
Via map, no place on the land selected: No teleport allowed
Via map, particular place on the land selected: No teleport allowed
Via landmark: No teleport allowed
"Landing Point":
Via OSW beacon: Landing Point
Via hop address without coordinates: Landing Point
Via hop address with coordinates: Landing Point
Via map, no place on the land selected: Landing Point
Via map, particular place on the land selected: Landing Point
Via landmark: Landing Point
"Anywhere":
Via OSW beacon: Landing Point
Via hop address without coordinates: Landing Point
Via hop address with coordinates: Coordinates at the end of the hop address
Via map, no place on the land selected: Landing Point
Via map, particular place on the land selected: Selected place
Via landmark: Landmark coordinates
So when should you pick what?
"Blocked" is for if you don't want avatars to teleport in at all. If you want them to enter by walking or riding a horse or use a scripted ferry boat or something like this, but they must not teleport. Don't use it for private parcels/sims! For that, go to "Access" and uncheck "Anyone can visit".
"Anywhere" is the recommended setting. It lets avatars with landmarks land where they've taken their landmarks, and it has those who come through OpenSimWorld land where it's appropriate.
"Landing Point" is for forcing all avatars to land at your pre-defined landing point, no matter what. Only use this setting if it's really important to have everyone land at the same spot. That could be a role-playing/adventure sim with a pre-defined starting point, a story-telling sim (unless the story is so long that people are tempted to use landmarks like bookmarks in a book so they can come back later), a maze, any kind of parcours or your personal land where you want visitors to land at the entrance rather than in your bedroom or on your secret sky platform.
Do not use "Landing Point" for exploration sims or for shopping/freebie sims! And do not use "Landing Point" for party sims either! Yes, it may be convenient for visitors to land right next to the dancefloor. But not everybody wants to be FORCED HARD to land there. Some of us prefer to land somewhere more natural/somewhere where they can't be seen rezzing and then walk to the party location. If "Teleport Routing" is set to "Landing Point", they can't do that.
Troubleshooting Q&A:
Q: My visitors always land in the water!
A: That's because you have water at 128, 128, x, and you don't have a landing point set for your sim. Find a good landing spot for your visitors. Go there with your avatar. Turn your avatar so you're facing into the right direction. Open the settings as described above. Under "Landing Point" (see the red box), click "Set". Under "Teleport Routing" (see the blue box), pick "Anywhere" if you want to allow avatars with landmarks to land somewhere else or "Landing Point" if you want absolutely everyone to always land at the landing spot you've selected.
Q: My visitors complain that their landmarks don't work; they're always forced to land in one particular spot on my sim!
A: That's because you've set "Teleport Routing" to "Landing Point". Switch it to "Anywhere".