A drop-down menu in the user interface is designed to expand when clicked and present a range of options. This is fine for country selection or customization, where there genuinely are lots of options.

There is, however, an overhead to operating a drop-down menu: the user needs to click to open, scroll to the correct item, then click to select. On a mobile device this can be even slower, as the user will be using a smaller screen.

If you only have two or three options, then don't jump to using a drop-down straightaway. Consider the options could be better presented to users with a different kind of control (radio buttons, sliders, and so on).

Sort your options into a sensible order—alphabetical or numeric—rather than random. Don't be the app that asks users to select a floor of a building in alphabetical order: "First, Fourth, Ground, Second, Third." Yes, I've seen this!

Very long drop-downs—for example, country selection—can benefit from a mini search or filter control: begin typing "U" and only see "Ukraine, United Arab Emirates, United Kingdom" and so on. This allows your user to skip to the section they need.

Mobile users actually have a head start here: most mobile operating systems will show a full-width "picker" control for drop-down selection, which is much less fiddly to use on a small touchscreen: