It's probably easier if you turn on "Ignore Backfacing". It's a checkbox option towards the top of the polygon parameters area. If this is checked, your less likely to select or deselect something you don't want to
If you have trouble deselecting the mouth faces, try going inside the back of the head. You'll be able to see some of the mouth faces much easier this way.
When you think you've got all of the inner eye and mouth faces deselected zoom back out and look around the whole head to make sure you haven't accidentally deselected some faces on the back of the head or something. Reselect any faces you need to and once you're sure you've got them all apply another UVW Mapping modifier. (click on the Modifier List Drop-Down menu above the modifier stack and scroll way down)
Just like before set Mapping to Cylindrical, and change the algnment until the cylinder is facing up and down
Click the button called "Fit" directly under alignment. This will fit the cylinder to the head in this axis. Next expand the + in front of UVW Mapping and select the Gizmo. Now scale the gizmo so that the checkers are squares
I often rotate the cylinder a little when I do the actual face. I try to meet the angle of the face a little like the image above.
Next right-click on the UVW Mapping modifier and choose Collapse All. Go back into Polygon select mode and scroll down to the Polygon Properties / Material ID section and set the material ID of the face polys to 9.
Now we need the remaining polys to be selected (the inner eyes and inner mouth). The easiest way I see at this point is to selection inversion (Edit > Select Invert) and then deselect the neck polys manually. This way all that's left are the inner eyes and mouth
These polys won't really be seen in any sort of clear way so we don't need to pay attention to their maping much. This is mostly just to keep them seperate from the rest of the face.
Click on the Modifier List and scroll down to UVW Mapping. This time we'll stick with a regular Planer map, so you don't need to change anything. Just right-click on UVW Mapping and collapse the stack. Go back into Polygon mode, scroll down, and set the Material ID of these faces to 8.
Now we've setup the mapping the entire face. Next is to lay it out in the unwrapper.
Click on the Modifier List drop-down menu again and this time choose Unwrap UVW.
Extend the + under Unwrap UVW to see the Select Face option. Now below the modifier stack in Selection Parameters find the thing that says Select MatID. Type in 9 and press the button. It selected the face! (Now you see why we set this up! It makes it so much easier to select these things).
Under Parameters click the BIG Edit button. This will open up the Unwrap editor window.
It's sort of a cluttered mess at first and it's hard to figure out what's what - especially with that checkboard texture in the background. There's a small button along the top bar of the Edit UVWs window that looks just like the checkered box we saw in the Material Editor. Click on this button once and it'll turn off the checkboard background image. Now it'll be much easier to see.
Choose the move tool and move the face UVs out of the 1x1 box (that's the square that everything is inside right now. Back over in the Selection Parameters section, type in 10 in the Select MatID box and click the button. Now the neck is selected. Drag it off to the side so that it's not overlapping anything.
And finally select the eye and mouth stuff and pull it off somewhere too
Lets deal with the eye and mouth stuff first. The eyes should be identicle to each other. Select one of them and go to Tools > Flip Horizontal. Now move the eye over top of the other one so they are taking up the same mapping space. If you want, you can drag a selection around both eyes and press Ctrl+W to weld them together