Khaios, you're always so generous with your tips and advice, it's really wonderful to see. Just wanted to give you that comment in addition to clicking the 'like' button.Hmmm. I guess my biggest suggestion is to be willing to experiment. If I have an idea for a build, and I have no idea how to accomplish it, I will try anything I can think of to get there. Sometimes I succeed, sometimes I fail, sometimes I learn a new trick that doesn't exactly help me for the project, but is extremely useful for others. Don't be afraid to break out of your comfort zones, and try new things. Accepting player build requests is pretty helpful for this. If you get some of the more cliche requests, try and think of a way to make them unique to you. I often get castle and angler house requests, so I try to make them as different as possible.
Google is your friend. Use it well! If I ever need inspiration, or if I'm attempting to build a style of structure I've never attempted before, I will frequently use google to find images to give me ideas of my own. Also, looking at what other people have built on Terraria is a fantastic way of learning new tricks. I don't recommend directly copying their work (without permission), but if you see that they've done something that looks great, but you have no idea how they did it, just ask! Every builder I know would be happy to share. Not all of my special tricks were developed by me. I've learned quite a lot from the Terraria community.
Now for a few bits of advice more directly related to building, I guess, haha. Never underestimate the value of paint and actuators. Paint can make nearly any type of wood look relatively close, and can give you new "stone" looking options. It can also be used to make actuated items look closer to being "active." If you actuate stone slab, for instance, then paint it white, it will look similar to a normal stone slab block.
Actuators are amazing for creating window frames, pillars, and supports. There are other great uses of them, so just play around with it! Pumpkin block holds paint extremely well, and gives a fabric appearance. When placed on the sides of a window, they look like drapes. Actuate them, and they can be freely walked in front of. Some hammer platforms are a great way to "hold" those drapes up. One warning about actuators. If you are using them inside a house, make sure there are background walls behind them. An actuated block does not count as a wall, and may ruin the validity of your housing, or allow monsters to spawn inside (they can spawn in front of actuated blocks, as long as there isn't a background wall behind them).
Windows don't just have to be glass walls. Fences of all types work equally well, and you can even leave gaps without losing the validity of your housing, as long as the gap in the walls is no longer or taller than four blocks. Just be warned that if you choose to leave holes, monsters can spawn inside of them, so during a blood moon, regardless of your friendly npc's, you may get monsters inside your house.
Don't use only one type of material for a build (personal preference). My floors are almost never the same materials as my walls and ceilings. Usually, my floors will contain two material types, and my ceilings may as well. I personally prefer the floor and ceiling to be two thick, and walls to be two (or sometimes three) blocks thick, unless the build is very tiny. Find out what works well together, experiment with what blocks blend, and what blocks do not. Sometimes it looks better to have them blend, and sometimes it looks better if they have a definite line. That's up to you! Blocks hammered in half will always blend into the block below them (even if the blocks naturally do not blend with each other), and ones hammered to an angle will always blend with the block above and/or the block below them, but not the block to the side (unless the block types blend normally).
I could go on for days, but this is already TL;DR worthy, so I'll end it now. Hope some of this mumbo jumbo could prove useful to you ^.^