There’s a few famous books out there about designing things for usability. The Design of Everyday Things is all about designing physical objects in a way that removes ambiguity and essentially, makes it impossible to use the object the wrong way. Don’t Make Me Think is all about web design and usability, and is handy for other aspects of interface design for computer programs.
Video game interfaces, meanwhile, have some additional complications. A lot of games strive to be immersive, and have minimal interfaces, often incorporating the elements you interact with directly into the world. Often, the interface can be used to enhance the gameplay when this is done well. Other times, the game is almost entirely interface, and the graphics are mostly to prevent the whole thing from being a giant mess of numbers.
Most tycoon style games go for something in between, with the game world being front and center, but with the ability to pull up all sorts of charts, graphs, and numbers. But the important numbers will be visible at all times, such as Sim City’s RCI indicator always being on screen, or Prison Architect’s temperature meter.
I have a philosophy of “don’t make me click”. Actions in the game should take the least number of clicks, in order of their importance. If something is done a lot, it should only take one click to do. If it’s a bit less common, then it can take a few clicks to do. I’m still working out exactly what the important numbers are for Isotower. Money, population, and overall rating are the current important bits, with time and weather also taking a place of importance. After that are tools to let the player design and build their tower, and finally the various details for individual rooms and visitors and residents of the tower.
Unfortunately, until the majority of the game is done, I don’t have a solid idea of what is going to be important and what isn’t. So the interface is going to be very rough until more pieces of the game are in place.