About of 15 percent of the population worldwide are left-handed. That is a huge number of people and potential customers, but their needs sometimes are not taken into consideration. Some interfaces and control elements are created mostly for right-handed persons (control elements are aligned to the right-hand side of the screen, which is especially evident when a device is in a landscape mode), and that is wrong. Especially when UIs are created for mobile devices with a very flexible layout system. To prepare a game which is handedness friendly, you only need to prepare two layouts of the buttons with their positions mirrored. By default, the layout for right-handed players should be used, but in the Options menu there must be a button to switch it to the left-handed setup. In most cases, such an approach can be developed very simply, because there is no need to redraw control elements and so on, only their coordinates need to be changed on the screen. Another approach is to try to develop a center-based UI or control system without an exact screen position (the application only needs to get a tap or gestures, but the exact coordinates are irrelevant), so it can be handedness independent, but that is not always possible.

If a game uses some specific gestures such as swipes, they should be comfortable for both types of handedness. An optimal solution is a vertical direction of such gestures, which is pretty comfortable for both hands; in case they are horizontal, it is good to keep in mind that a direction towards the dominating hand is more comfortable for people.

And as always, it's very important to have a real left-handed person, who can share his thoughts about the UI adaptations for his needs.