I got it. In order to make some practice, i'm doing a treasure box, where a lot of elements are supposed to repeat.
Is there some easy and effective way to overlap UVs without mistakes?
For example, the top of the box is supposed to repeat, now: do i have to take and manually move the selected piece above the upper one, and so one until i have all four pieces one upper another? It's difficult to have pixel-precision with free hand.
Oh, and another thing: for example, iif a have to draw an entire wall with a flat pattern, it is possibile to have, let's say, only 10 pixel of pattern on the UV and then make it repeat (Tile it) on the plane, instead of having just one all distorted?
Well, I don't know what software you're using, but both Maya and XSI, that I used, have snap functions for UVs as well as align options. Like, drag all the squares to roughly the same area, then select left side, align to left, select right side, align to right, and repeat for up and down. Or, if that option exists, select all left corners and snap to grid, or something, then snap another corner to another point in the grid. Whatever works. It's just a matter of learning the tools you're using, and I'm afraid I don't know yours.
As for repeating UVs... Yes, and no. If you want an entire object, say a building, to use only one texture file, then you need as many subdivisions in the surface that you want to tile, as times you want the textures to tile, so you can overlap all those UVs. But that's very inefficient and I wouldn't recommend it. The only way to have it tile like that is to have one surface or object use a stand-alone, tiling texture file. Like if you have a 64x64 that is only one wall texture that repeats in all four directions. If you do that, you can scale the UV up to be larger than the size of the texture, and that'll make it repeat. Like, if the UV is twice as big as the texture in the UV window, then the texture will repeat itself twice for that space on the model. But again, that only works if the texture itself tiles seamlessly and can't be done if you want a unique texture for each object.
Often, for low-poly, low-res stuff, what you can do is sacrifice some polygons for the sake of preserving texture space. Like, if you have a house there... I think that's what it's supposed to be... You could add one more edgeloop along the longest side. That way those awkward, elongated walls will turn into two nice squares that you can overlap, and at least have the texture repeat once. Usually, texture memory is much, much more important than polycount if you want to stay true to old system restrictions, or things like the DS and iPhone. But now we're really touching on the finer sides of low-res modelling and texturing, here. The whole concept of balancing between a clean mesh and a compact UV is an art in itself. There's a lot more information and inspiration for this stuff on a site like
Polycount, as much as I hate to plug another forum on here! But I've noticed we do share a lot of members. Maybe I can consider it a sister site-in-law of Pixelation or something.