To get better texture resolution, people tend to make things more modular. For instance your building facia there might be made from two modular pieces. So you’d do a “window” piece and a “door” piece and texture those up appropriately. You might also consider tiled textures in parts too.
There’s no magic to this though, go to any 3D tutorial site (3dtotal.com 3dbuzz.com cgtutors.com eat3d.com) and learn.