A picture shelf is a great way to give uniformity to your arrangement. Note that they have stuck with black and white photographs, mats, and frames. The varying sizes of mat white space keep it interesting.
Here a variety of pieces mix well; letters and postcards fill in space between framed artwork.
I'm trying to figure out why this works so well. I think it's the balance between height and width - some are wider than they are tall and vice-versa, and they are placed just right in relation to one another.
This is some sort of black and white Hollywood glam family tree arrangement
Don't forget that objects you might not usually consider as art can make for a delightful arrangement.
A collection can be playfully arranged in a symmetrical grid pattern of frames to take on the appearance of art.
Don't forget about white space. The art stands out here because it's not too crowded.
This group all fits into a perfect large square. Put up painter's tape to mark your boundaries and then put up the frames within it to get this effect.
This one takes it to the next level. Add a grid of tape within the square to line things up properly.
Grouping frameless stretched canvases together gives a just enough of a feeling of uniformity.
From Victoria, arranging master and the one who set the Keep Calm and Carry on Trend. Note how these pieces float within the white frames and glass against the white wall.
I had to include one of my early attempts at arrangement from my shabby eclectic phase. Don't worry, this has changed since this was taken. For some reason I always seemed to include some crazy huge ashtray, a favorite purse, and an album from my teenage angst, in this case, The Smiths - Meat is Murder.