I haven't done anything with mobile. But I'm looking at taking a viewer for a 3D world and running it on mobile. (Probably via a cloud gaming server, but that's a side issue.) So, what should the user interface be like?

On desktop, it's arrow keys or WASD to move, plus you can zoom in with the mouse wheel. If you zoom in far enough, a targeting cursor appears and you can move that with the mouse. Straightforward.

What are the accepted conventions for doing that sort of thing on a phone? Moving around and looking around must be fluid and intuitive. For other stuff, there's menus.

The Call of Duty crowd seems to like to use game controllers on mobile, but this isn't a shooter, and I'd rather not go that far.

Tom Sloper said:
Use pinch/spread for the 3rd.

For more advanced movement, you can create a virtual analog thumbstick on touch. So if i press the thumb on display, nothing happens yet. If i slide a bit up or down - forward or backward; sliding left or right - strafing.
To stop, i lift the finger up and put it down again to be ready for the next move.

So you can divide the screen in two halfs horizontally. Left side for movement, right for mouselook. Works well and is intuitive. If you need a fire button as well, things become much worse.

What about tilting and aiming the phone? How does that work out in practice? A few games have used it.

Nagle said:
What about tilting and aiming the phone? How does that work out in practice? A few games have used it.

It's great for racing games, but for 3D navigation, where you need both dimensions, it's too hard to keep the phone in a fixed orientation when you want to keep looking straight.
And you have no option to ‘lift the mouse’, so you might need a virtual button to fix camera while rotating phone back to a relaxed position.
But try yourself what fits your needs, and ideally give options to the users.

I would say, if you want something like a shop for 3D items to browse them, use pinch and spread, because you can keep phone in usual portrait orientation, doing all interaction with the right hand, holding it with the left.
If you want to traverse 3D space, e.g. to visit virtual architecture, use my proposal, requiring both hands and holding the phone like a gamepad.

Sorry for the late reply, but there are no clearcut ways to do this. I usually finding mobile controls annoying. I did this for my RPG game engine: touching left side of the screen: left. Touching top: up. Touching bottom: down. Touching right side: right. Touching the middle of the screen: action. Some android devices have keyboards and/or cursor keys too, so those also must be supported (i did those as well).

But i have scrapped Android support, and in the future i am not going to compile anything for it. So its not a problem for me any more.