I find there are a few things you can do, that helps. (These coming from what has helped me, aka a bad builder)
1. The thing that helps me the most is prebuild it in a creative world. Yeah extra work and time, but if you really want something to come out right Pre build!
2. Sometimes it helps to build the inside first. So if your making your power room, figure out what you want in there, how much room you want between it all, how you want it layed out. Then build the walls around it.
3. If no building the inside first then find a building shape you like, build it and then fit your machines to it.
4. Accents! Don't use just 1 material. Use 2 bare minimum. For example, spruce (Dark wood) walls and floors, with a cobble stair roof looks just fine. If you can throw in 3-4 materials then thats better. If your building from wood, outline a few things, say the corners of the house and the doors with logs, make the floor have a nice pattern.
5. And my last tip, Build in 3D! This is minecraft after all, you have 3D to work with, there is no reason why all your buildings should be flat walls, flat roof, flat floor. Throw a few support pillars out sides to hold up your walls, make your roof a stair way up so its not flat, Don't forget about giving that roof a 1 block overhang though, that helps a lot. Make the floor out of half slabs and then maybe put each chest up on a little podium.
So to recap, Prebuild! Make the building fit the rooms, or make the rooms fit the building! Use more then 1 building material! 2 is bare minimum. Dont build flat!