Looks like you'll either have to deal with some squash in the indents or stretching on the larger surface area. OR you could detach the indents and relax them separately but that will create more UV edges and more verts overall once you get it in game. BUT you could stack all of the indents on top of each other and save some UV space.
Personally I'd probably just squash the indents a little, and stretch the larger surface area, and think about mirroring it all, but that depends on the kind of detail you have planned.
This is my first time UV mapping and I dunno if I am doing it right, because, I have a few questions.. first, do I need to arrange my mesh inside the UV texture editor's grid? and, what do you think of what I did so far, what is wrong, what could I change, etc.. ??
That's not bad at all, although you could spend a little more time trying to maximise your use of the space. As far as arranging the layout, it all needs to go into the 0 to 1 space, which is the top right quarter shown in your screenshot.
There's a couple of areas that have a few squashed or distorted UVs. The grip looks like it's just been planar mapped, so the faces around the inner and outer edges are squashed. Select all the UVs on the grip then click the "smooth UV" button (see screenshot). Then click and drag the "unfold" button to the right a few times. You might need to split the UV's along the mirrored edges for this to work properly. I'd also split the sides off that litte bit connecting the grip to the rest of the gun and either unfold or remap it.
In case you don't know this already, you can quickly select a UV shell by slecting a single uv from it, then hold Ctrl+right click and "select shell" from the marking menu that appears.
It's not perfect, but it's nearly good enough for a first attempt. Try repeating the process you used on the grip to fix the inner/outer faces on the trigger guard. I revised the screenshot above with a couple more splits, which should help to straighten out the bit at the top of the gun. Make the splits and again use the unfold button as before.
What you're aiming for on a hard surface object like this is to try to keep as many of the straight edges either perfectly vertical or horizontal as it's much easier to work with and will give you crisper results once painted. The higher the resolution of your final texture, the less it matters. If you're working with a low-res texture, you'll get obvious stair-stepping on any diagonal lines. Hope that makes some kind of sense.
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Personally I'd probably just squash the indents a little, and stretch the larger surface area, and think about mirroring it all, but that depends on the kind of detail you have planned.
But I'd try to mirror the sides. As in have a few strips in the middle to cover up the mirrored look, yet saving texture space by only having 1 side texture.
Vig:
couldn't he still just slice up the cylinder texture in 6,3 or 2 parts? No need to detach the indents for that, I think.
There's a couple of areas that have a few squashed or distorted UVs. The grip looks like it's just been planar mapped, so the faces around the inner and outer edges are squashed. Select all the UVs on the grip then click the "smooth UV" button (see screenshot). Then click and drag the "unfold" button to the right a few times. You might need to split the UV's along the mirrored edges for this to work properly. I'd also split the sides off that litte bit connecting the grip to the rest of the gun and either unfold or remap it.
In case you don't know this already, you can quickly select a UV shell by slecting a single uv from it, then hold Ctrl+right click and "select shell" from the marking menu that appears.
Oh and I also want to know if there is any better way of UV mapping the trigger guard.. I had some difficulties trying to make it in one piece.. =[
What you're aiming for on a hard surface object like this is to try to keep as many of the straight edges either perfectly vertical or horizontal as it's much easier to work with and will give you crisper results once painted. The higher the resolution of your final texture, the less it matters. If you're working with a low-res texture, you'll get obvious stair-stepping on any diagonal lines. Hope that makes some kind of sense.