I've been playing Minecraft since 2011/2012 somewhere around that time and my smol brain still can't figure out how to build something that looks even semi-decent. I want to build an underground facility but for those of you that have a seen my base before you would know it is an absolute mess. Anybody got any ideas or ways to practice building on Minecraft?
In regards to actually building things, plan it out. Tell yourself, "In this room, what do I want to have? Smelting? Magic?" Once you figure that out, put down your machines first. After that, build around it. This will help you for planning out how big you need to make rooms.
In regards to design, pick a theme and stick with it. Look at all the block options in NEI. Chisel Mod has a lot of options to pick from with most of them being very easy to make. Just make a bunch of them and play around with the designs a bit to find out what you're looking for.
After that, it's all about how you want your factory to be set up. Plan out some room layouts with connecting hallways. Maybe put a room that does nothing but appeals to the eyes? There are a lot of images of what others have made if you keep drawing a blank.
As far as practice is concerned, work on it on single player creative, so you know what you want to use. Having everything to use helps you make quicker decisions. Once you got all of your planning done, you just need to get the materials on the server before you begin.