Hammer the nail, hang the picture, step back, wince, repeat.
Deciding how to decorate a wall is the hardest part of arranging my house. If my couch looks obscene pushed against a wall, I can move it. But hanging up art leaves a mark. From many years of making holes for eye sores, I've come up with a formula that gets a very nice result. I was tinkering with Illustrator today and I drew out some of my thinking not required design techniques!
A Common Arrangement

[1] Exposed cords
[2] Art Hung too Low
[3] Cluttered Mega-frame
[4] Diagonal Hanging
[5] Small Frames on a big wall
[6] The Panties
First, you don't need exposed cords, ever. I've seen some scary things, like drooping extension cords taped to the ceiling, back in the days when I managed an apartment building. If you can neatly conceal the cord, you should. If you can't aesthetically justify it, then think about safety. There's nothing like tripping over a wire and ripping it out of the socket with a nice frightening spark to motivate you.
Second, hanging your art low on the wall might be convienient for hanging, but it usually dwarfs the room. Hanging things up high makes the room feel taller and less cluttered. The tops of your wall art should be very close to the height of your door frame. I usually go about 4 inches higher than the top of my door frames.
Third. The cluttered mega-frame. Not a strict no-no, but usually, these turn out underwhelming. Your favorite pictures get lost, and from a distance, they tend to just look muddy and tight.
Fourth. Hanging diagonally is an advanced skill. It only works well on small walls, like 2 feet wide, or on staircases. Usually it's just going to add an "invisible" line that leads the eye up to the ceiling and down toward the floor. A floor that might have your panties on it. It doesn't tend to compliment the space.
Fifth. Small, itty bitty frames on a big wall will make them look even tinier. You might think they are big, but seriously, even small walls are enormous compared to a 4 inch by 6 inch picture.
Sixth. Panties on the floor. Tsk tsk.
You might be thinking, "You bitch!" but relax - a lot of people can make some of these six things work. Except for the panties. I hope you ren't entirely offended if you have some of these things going on in your rooms. Some people can make low hung art work fantastically. It really depends on the room and decorator. Me? I'm not so good. I just want to brainlessly put up the art and call it a day.
Solution 1: Hang Tiny Frames as a Grid

Using some painter's tape and a laser leveller, you can hang all your tiny little frames together. This network of frames creates what feels like a big piece of art. Bonus points for matching the frames, and matching the photo styles (like all black and white, or all travel photos). Another variation is to hang up an eclectic mix of frames in more of an organic cloud. This works best if you have a mixture of truly gorgeous, bohemian frames. Not including oak frames with sayings like Fancy Pet! burned on. Frames with words are better as table top frames. Wall art should be visible and enjoyable several feet away, whereas things that people have to read are better off the walls.
Solution 2: Small picture, Big frames

Add a matting and a bigger frame, and suddenly that 4 by 6 picture stands out. The look is very complete. Additionally, it follows a common design rule: arrange in odd numbers. I like to arrange in prime numbers (which means odd plus 2 - not really prime). Things go in pairs or 3s or 5s.
Solution 3: Big Art!

Your walls are huge! Anything smaller than 24 inches will look really tiny. You will have trouble trying to hang up something little, but 2 big pieces are just about all a room often needs.
How Big Art Can go Bad: Matching framing to the picture

Not everyone will agree, but I find it less successful when people match the matting and framing to the picture. Your matting and framing should ideally coordinate with the rest of your matting and framing. See, the framing is to showcase the art - it's a non-distracting helper. Different colored matting and framing can often just highlight the helper. I have a variety of frame colors but I stick with whites and creams in matting.
Solution 4: Variety!

You can fit all sorts of weird shapes together. Notice that the tops and bottoms of all the pieces form an almost unified line. This is part of what helps it from getting too crazy.
How Variety can go Bad: Too Many Materials

You can definitely mix and match, but to a point. I have a variety of frames (silvers, ornate golds, woods and shells) and it helps to clump like frames together. If I have to mix and match, I make sure to include at least 2 that will go together. My favorite mix is to put ornate golds with bronzey woods. Right next to that I have groups of silvers - brush nickel and shell, then shiny shiny chromes. The frames just need to have 2 or 3 friends to not stick out.
Avoiding certain materials will make it easier over time: like colored plastics and white-washed woods (those will marry you to a style). Sticking to basic families (black, white, wood, gold or silver) will make it so much easier to update your style decade to decade. I have also picked a decorating metal: silver tones. Almost everything I have purchased in the last 4 years is silver toned (lamp bases, frames, blanket stands) so it's helped me unify the space without very much effort at all. I still have gold toned and even oil-rubbed bronze things but I think the silver dominence is paying off. I'm on design auto-pilot.
April 21 2008, 23:06:58 UTC 4 years ago
It makes me crazy but I can't stop her because it's in her areas/with her art.
April 21 2008, 23:35:20 UTC 4 years ago
April 21 2008, 23:13:43 UTC 4 years ago
Also, I would say that Big Gulp on the nightstand is a no-no, one time I left a Taco Bell cup up there and the condensation dribbled all over a good piece of furniture ;)
April 21 2008, 23:14:19 UTC 4 years ago
April 21 2008, 23:40:14 UTC 4 years ago
(Another tip - put up a little piece of painter's tape where you want your nail. Then nail through the tape. Your nail hole will often be smaller because the tape's slight tension is enough to keep most walls from cracking and making a looser hole)
April 21 2008, 23:15:09 UTC 4 years ago
April 21 2008, 23:23:16 UTC 4 years ago Edited: April 21 2008, 23:43:28 UTC
Do you have examples of heights that bug you? Maybe they will bug me too.
April 22 2008, 00:00:20 UTC 4 years ago
April 22 2008, 00:13:24 UTC 4 years ago
Nothing is weirder to my eyes than the random picture up above the door, jammed up to the ceiling, complimented by a low hung diagonal postcard trio.
April 22 2008, 00:15:58 UTC 4 years ago
April 22 2008, 00:42:06 UTC 4 years ago
April 22 2008, 15:28:55 UTC 4 years ago
April 22 2008, 16:00:13 UTC 4 years ago
Google "gallery hanging height". You want to actually look at and enjoy your art. I prefer it a bit lower over a sofa or a bed with a low (or no) headboard, because it helps with the massing.
April 22 2008, 16:55:02 UTC 4 years ago Edited: April 22 2008, 17:10:57 UTC
I don't think top of the door frame is way too high. Average door height is around 6'8"... that's 80 inches. Take your painting that is 36" long. We'll subtract half of that from 80 inches. That puts the center at 62" - so it's kind of a minimal difference in most cases.
It still depends on the wall height, door height and height of the furniture, as well as the art itself (and the planned hanging composition, oh and perhaps the presence of ornate crown moulding) - I don't think there's a universal rule that will always work. What doesn't work is scattering art around the room without any sense of cohesiveness.
April 23 2008, 12:11:06 UTC 4 years ago
April 21 2008, 23:45:42 UTC 4 years ago
I used to work in a frame store, and people would ask about that all the time. Who thinks hanging little trios about a sofa looks good?
April 21 2008, 23:51:13 UTC 4 years ago
April 22 2008, 00:29:40 UTC 4 years ago
Really, though, this is a helpful post--thanks!
April 22 2008, 01:16:54 UTC 4 years ago
April 22 2008, 03:04:32 UTC 4 years ago
thanks
April 22 2008, 03:44:47 UTC 4 years ago
*cries*
Anonymous
April 22 2008, 17:39:07 UTC 4 years ago
Height of hanging art
I think the reason so many are disagreeing with you height criteria is because you are measuring from the top of the art piece. Standard rule of thumb is to hang at "eye-level" measured from the CENTER of the art piece. Unframed posters can be hung a bit higher (though seriously, unless you're in college (or younger), who decorates with unframed posters?).April 22 2008, 17:47:55 UTC 4 years ago
Re: Height of hanging art
This guide isn't to establish a canon of techniques, but to offer some easy solutions for people who are agonizing over it. The math of using the door height and top of the piece as quick guides isn't extremely off the gallery canon. I think heights of furnishings and the wall itself can bump up the pieces without taking them dramatically out of eye-level.April 23 2008, 06:02:54 UTC 4 years ago
July 1 2008, 23:38:10 UTC 3 years ago
Thanks!