start simple! use references to help, whether it be real structures or other builds. one thing that helps if you're looking to practice gradients as finnodile said below is build a 3 by 3 square and try to find blocks that fit well with it.
also, don't hesitate to use nonconventional blocks! use a composter in something brown to bring life, or use a crafter or a smoker for that little bit of extra texture.
most importantly, start small. you don't need to build giant houses to be good. start with a little cottage, and work your way up.
