When using Blender for small UV layouts, there are a few tricks you can do to save space and get the pixels looking nice and square / uniform:
1) If you use a mirror modifier for the model, you can unwrap the model before you apply the modifier. This will let you unwrap only half the model and mirror the texture to the other half. The downside to this is that any text from one side will be reversed on the other side. You can get around this by applying the mirror and then editing the UV layout for the faces you want to edit. Very useful technique if you want to make a character with an asymetrical face or some other asymetrical aspects, but with other areas mirrored on both sides. Another downside to this might be the fact that mirroring this way requires that there be a seam running down the middle of your model, which can add to the geometry. If you have a very square model, it might seem a waste of polygons. There are some methods to avoid the extra geometry, but they would require more texture space and a bit of extra unwrapping to get rid of the seam.
2) There is an option called "Snap to Pixels" that will snap the verts to the corners of the pixels, allowing you to get perfectly square areas to have perfectly square textures. Snapping takes some practice, tho, as you can easilly end up with warping if the shape of the face in the UV editor is too far off from it's shape on the 3D view. For really low-res models, these little warps can draw a lot of attention to themselves. I'd recomend snapping to pixels to do the layout, getting the basic layout down and then turning that feature off and making adjustments to minimize any warping going on. Snapping is incredibly useful on some models. Especially models that are very boxy or that are extremely low-poly. Try to keep the UV islands as simple as possible, with few polys per island. Makes it easier to prevent warping and easier to conserve and re-use texture space.
3) When I unwrap a very low-poly model like this, I tend to pin (p key) all the verts after I unwrap it, and then if you need to edit the seams at all, unpin the areas you need to alter in the layout and unwrap it again. You'll have to scale them down to fit (Blender will unwrap anything to make use of the full UV space, ignoring any bits of the layout that were unchanged), but you'll be able to alter parts of the layout that way without losing all your work in the other areas of the layout. Especially useful if you have those areas textured already and don't want to have to waste time re-texturing those parts, or re-fitting the islands to them. Especially useful if you are trying to add some asymetrical details to sections of the model while other sections are mirrored.