How to have good game graphics on many different screen resolutions?

easiest method.... pick device with highest resolution... build graphics at that res.... then it will look pretty good on all..... but your assets may be oversized and use too much memory on most devices... Typical solution.... is LOD (Level of Detail) have different versions of assets that you load, depending on device resolution. They could be different prefabs, or different textures you load in from resources folders, or one whole bundle of assets that you stream/download the first time a user runs a game. (typically, for mobile, you'd have 2 or 3 levels of detail)