I just start building, using the right lot size and build-mode grid are helpful. I’ve only built a few things inspired by real homes/building; sometimes if I get an idea I also look up what other sim builders have done. Another thing that I think helps me is when I build I also place basic items like counters and bookcases in rooms just to see if an area is too big or too small, then can add or shrink the space. I think it helps to know all the cheats in building as well, for me anyway.