Youssarian's Guide to Making Stuff Look Good
It seems like the main goal of making stuff look good in Minecraft is to avoid straight lines at all costs. Even though rooms may have a rectangular shape, the building as a whole ought not be rectangular, unless it's a minor building. The method I'm developing relies on these sort of rules I've learned. They may differ from what the videos and pictures have taught me, but that's just to have a personalized style.
First, it picking colors. You can choose colors that complement each other, or contrast. Colors that complement each other are similar in color. For example, lapis blocks and purple wool. Similar in color that they could go well together. Also consider emerald blocks and the pukey yellow wool. Birch planks and sandstone seem like they would fall under the category of complements, although I could also see why they might be contrasts. Here are some examples of complementing blocks:
The contrasting colors are ones that seem opposite in the color spectrum. An easy example would be black and white. Obsidian is dark enough a blue that it contrasts well with snow. Likewise, the darker spruce wood contrasts well with white wool, snow, or things of that color. I've noticed that a wall of stone brick with a cobblestone pattern inside it looks wonderful. Mojang did a good job at finding a way to make cobble look alright.
Once you have a theme, a group of blocks you want to work with, it's time to start looking at the overall design. For the exterior, I'm able to sort of do it systematically.
Normally I build the front wall first, and generally it's either 8 or 13 blocks wide. There's something called the Golden Ratio, which is a number which people have seen for centuries as the best ratio of line lengths for beauty. In Minecraft, this can best be approximated using a series of numbers called the Fibonacci numbers. The first few are 1, 1, 2, 3, 5, 8, 13, and 21. Each number is the addition of the two behind it. So for my bog standard build, I'll make, say, an 8x13 house. A one-floor building will typically be 4 blocks high so it doesn't feel cramped indoors, but if you want to keep using the Fibonacci numbers, the height should be 5. Here is the outline of a 13x8x4 house. It will be used in further examples.
Something I learned is that blocks, depending on their texture, have something called movement, although I like to call it energy. Based upon their texture, they may seem to have vertical, horizontal, or neutral energy. Here's what I mean.
Blocks that have vertical energy include logs, melons, the sides of pumpkins, and chiseled smoothstone. Their textures seem to have a predominantly up-down direction to them. Logs in particular have this, which explains why they're so often favored as corner materials. Now even though I would argue that jungle and birch wood have more of a horizontal energy, we're so accustomed to using logs as edges that they would be acceptable.
Horizontal energy can be found in a lot of blocks. Double stone slabs are an example of horizontal energy and although many might disagree with me, I feel as though planks and wool also have horizontal energy. Smoothstone also has a bit of horizontal energy. Their textures are predominantly left-to-right in the default texture pack. Sideways logs are other examples.
Then there are blocks which don't exhibit much of any kind of motion or energy. You might consider dirt, sand, snow, lapis blocks, obsidian, emerald blocks, brick, and stone brick to be neutral. These are good for filling in walls or when you want to switch from one energy to another.
The way I typically design the exterior of a wall is this: I put blocks with horizontal energy along the top and bottom, blocks with vertical energy on the sides, then use neutral blocks in the corners where the two energies meet, and also as the main block that fills in the wall. This just looks right for me.
Note that the feelings of motion and what kind of blocks should be used where is, to an extent, subjective. I suppose many combinations that disregard these rules would look good.
Walls and floors can be improved by adding patterns. Something I might do for a living room is have the outline of the floor be whatever the bottom border block was, then fill the floor with some kind of checkered pattern, or something else. Likewise with the ceiling. Note that roofs are still a bit of a challenge for me. I may do a future revision of this guide, with some tips for roofs.
In order to escape the habit of making straight lines excessively, There are some things you could do. For instance, consider curving part or all of a wall so you have an alcove or some kind of semicircle. Experiment with it until you feel alright with it not being too pointy but not too flat. This is one of those things that is about personal preference. Most people won't be impressed by the exact arrangement as much as just seeing some curvature.
A fancy trick I encountered was instead of just building a pillar up for, say, an entrance, you might consider a diagonal side. Diagonals are sort of straight lines so if overused, they give blandness. Even better, you could take it into the third dimension, as advised below, and have the pillar point toward or away from the player. Here is something I made that's been sitting on my creative map.
Also useful are half slabs and stairs. When they first made it possible to place slabs and stairs upside down, I couldn't see the use in it. Now I'm glad they did, because it does a good job of breaking straight lines. They can be used to make arches, for instance. Alternatively they may act as extensions for support pillars. Half slabs serve as nice overhangs.
Next piece of advice: take it to the third dimension! This is where the decorative blocks, which I define as ones that aren't your standard size, come in to play. I'm talking glass panes, half slabs, stairs, saplings, ferns, flowers, fences, paintings, beds, and so on. Trapdoors are classic shutters. Fences may be used as support pillars. Panes make for excellent windows as they are thin and flexible in shape. I would recommend using them instead of standard glass blocks whenever possible. Buttons look good even if they're just sitting there. Look for safe ways to include fire, lava, and water, since they have moving textures. Adding these small things break up the otherwise blocky feel of a building. Redstone wire doesn't have much appeal to me as anything except a functional block. Also remember to try including furniture on the inside, if it's appropriate.
If you want to make the house look realistic, check out buildings similar to it. Pretend the law of gravity can pull down all of the blocks unless they had a good support system. By doing this you'll probably end up adding support pillars, maybe even changing block choice for realism. The basement of a house tends to be concrete, not sponge; likewise, glass won't hold up the side of a building.
Windows are good to have. Small wooden huts feel a lot more open when there are windows.
I added these shutters after I finished the tutorial. They add to the third dimension aspect:
Lastly, consider implementing things that need to be made up of blocks. That's kind of vague, so here's an example: banners. Wool banners hanging from the ceiling, anchored to fences. Give that sort of RP, pretend feel a spin. For example, here's an antenna found on house roofs for getting channels broadcasted through the air.
The key to developing a style, outside of reading and observing others, is to experiment. Don't be afraid of asymmetry. Do a little pattern variation here and there.
The example house I made here may not come off as the most elegant one ever made. That's because I'm still learning how to do this. But I hope that what I've presented here is enough to help others like me get an idea how to make stuff that looks alright. No more cobblestone huts for us; now we are equipped with the basic skills to build an appreciable home.