Next is the torso
For the torso, we'll do it a little different. Instead of unwrapping and then adding symmetry on top, we'll unwrap the whole torso already mirrored. So you can right-click on the symmetry modifier and collapse all right now.
It's a lot easier to hide symmetrical textures on the legs or shoes then it is to hide them on the front of a shirt. Perfectly symmetrical cloth wrinkles on a shirt front often look bad, so we're only going to mirror portions of the texture.
Start out by putting an Unwrap UVW modifier on the torso, expand the + sign so you can select Face, select the entire model and click the Cylindrical button. Move and Scale the gizmo so that it fits the torso as best as possible.
Next change to Vertices select mode, and click the Edit button.
My plan is to mirror the sides and the back, but leave the front as it is. First I selected half the back, detached it (Ctrl+D) and then Flipped it horizontally and moved it over top of the other half of the back.
Next I selected the half of the side on the right that I wanted to share UVs with the other half. I Detached them (Ctrl+D) Flipped them horizontally, and moved them over to the portion of the other side that matched them.
There was one more thing I needed to tweak on it before I could consider it done. The faces that make up the shoulder are very small in the UV unwrap because they're at an angle from where the projection was coming from,
so they're very stretched in comparison to the rest. So I selected the verts of the collar and pulled them upwards to increase the length of the UVs for the shoulders.
Once I'm satisfied with the unwrap I fit it into the square, render a UV image, save it, close the edit window, and right-click on the Unwrap UVW modifier and choose Collapse All.
And now we move onto the Arm
So select the arm. It should be by itself since we detached it from the torso. You can wait until you're done with the unwrapping to put a symmetry modifier on it. For now put the Unwrap UVW modifier on it from the Modifier List, expand the + and click Face selection mode and select the entire arm.
Click the Cylindrical button. None of the automatic axis will actually line up with the arm's angle. Instead rotate and move the gizmo until it's about the correct angle and then click the Fit button and it'll hug the arm better. Check from multiple angles to see if you're getting the best angle on the arm.
Also remember to scale (make sure it's set to scale on Local Axis) so the checkers are closer to square.
When you've got the gizmo to the best size and shape you can, click the cylindrical button again to deactivate it and click the edit button to open the UV Edit window.
Just like with the pants, the edge that's in the center of the inner side is the one that we want the seam to fall on.
Go to vertices selection and select any faces that are on the wrong side of the seam that should be on the other
side, Detach (Ctrl+D) and Move them to the other side.
Clean up any stretching or squished areas, and when you're done, freeform transform it into the square, render the UV texture out, save it, close the edit window, and collapse the stack.