Your game’s user interface is a critical part of the gaming experience, and its design will impact gameplay by a large margin. The things that you emphasize in the UI and its ease of use can easily make or break the player’s experience. There are many key factors in creating a successful interface, so let's get started on a few.
Make sure to implement proper "call to actions" appropriately at each part of the game— even in the menus. A player who doesn’t know what to do is an unhappy player. Give the player a basic guideline on what needs to be done, and where, and let them settle the method of accomplishing that. Of course, not every game needs direction, such as in some sandbox games, but even open-world games can benefit from markers to show quest locations or other points of interest or low health indicators to provoke a response to heal.
In the design of it itself, don’t break immersion. Make sure your UI matches the style of your game, because after all, your UI isn’t the point of the game, the game is. The best UI, no matter how visually appealing it is, will be function and subservient to the game itself. It accentuates the game’s design yet doesn’t distract from it. As a side note, if you’re building a game that will have both a mobile port and a port on other devices, or will have one in the future, make sure to start with the mobile’s UI and enhance it for larger screens where needed. I’s a lot harder to move in the opposite direction. One thing to consider though when porting a mobile game to PC though is the importance of making sure that the UI doesn’t scream out lazy mobile port.
In terms of visuals, restrict the color palette and don’t rely on color alone to convey meaning. If your UI is too busy, it can be hard to interpret when things are getting intense, or might take longer than desired for a person to look at and interpret meaning. Similarly, if you’re using colors alone to convey meaning, colorblindness is a huge handicap. There’s lots of ways to test if you’re relying too much on the color, but viewing the UI in grayscale is a simple, quick method to see if it works. Use other methods such as size, contrast, shape, orientation, and text to convey meaning beyond just color.
With regards to text, if you ever plan on translating the game, give the UI plenty of room to breathe. Some translations can make your text 2–3 times larger, so design accordingly and make sure you have enough room. Also keep in mind that left to right won’t always be the way it is read; other languages can read right to left and in columns. Make sure you’re not leaving in “strange” looking or sounding text, such as slang, awkward wording, typos, or blocks of text.
If you plan on having icons, be careful and make sure the player actually understands what they mean. They’re a good way to simplify your text, but many icons are completely arbitrary representations of ideas, and as a result the user may not have experience with them and won’t understand their meaning. Reading text will always be faster than icon interpretation, at least on a first-time basis. Ideally, you should have icons beside text on shortcut menus then allow the user to collapse the text at their discretion once they have a sufficient understanding of the interface. If nothing else, give the player tooltips so they don’t have to guess their way through the UI. I have seen various YouTubers time and time again fail to correctly interpret a stat on a car in racing games or some stat on a weapon in shooters due to the icon being a spring or a magazine without any actual explanation of what those things represent. Also, make sure there is enough contrast between your text and the background so that it can be distinguished quickly.
Important Takeaways: Your game’s user interface, is a key factor in making the player’s experience a positive one. Don’t break immersion. Make sure to restrict its color palette, and don’t rely on color alone to convey meaning. Avoid “strange” text, make sure icons are properly defined, keep it consistent, and ensure that it is responsive. You want to make sure it is easy to interpret and visually fitting for the game. Don’t try to make your UI look obnoxiously fancy in an experimental way unless that particular design has been extensively tested and proven to be better and easier to use and master than the industry standard. The same concept applies to text. When in doubt, utilize the power of playtesters. Watch how the interface is used and where and when players get frustrated — you’ll be able to quickly recognize the pain points and iterate accordingly.