STEP BY STEP
UNWRAP A HUMAN MODEL IN RIZOMUV
01 SQUARE HEAD
To make your head square after cutting it, start by setting constraints: in Rizomuv, put a vertical constraint (ALT+V) on each side and a horizontal (ALT+T) one on top. Then run an optimise, not an unwrap, as it's ‘gentler’ on the new shape. Also, note that the Optimise function does not keep the brushwork, so save brushwork for last. Use the Optimise (F7), Pinch (CTRL+F11), and Spread (F11) brushes to get rid of remaining distortion.
02 HANDS
Hands are often finicky to unwrap. Try unwrapping them in one piece, and if they are mirrored and identical, use the Symmetry tool to unwrap one hand only. Then use the Magic Wand tool to cookiecut nails away from the hand(s), as well as the hands themselves. It's much easier using the sliders to cut out i.e. the outer hand and generating cuts that way, than selecting, tweaking, then cutting edges.
03 STACKING
Stacking UV islands saves you lots of UV space. In Rizomuv, you can stack several ways: left and bottom align a set of non-identical islands and group them by pressing G, or use the Stack (Shift+c) or Stack and Group (ALT+G) options together with Topocopy, to stack.
For any hair or fur cards, use rectangularise to straighten them before stacking, and use the cylinder Autoseam option to cut and pack cylindrical shapes, like tassels.
04 AUTOSEAMS
If your model is hard to work with, try using Autoseams with the attract/ protect brush. This also works well on bad geometry, humanoids included. It's intended to be used with Autoseams, and you paint green areas to allow seams and red areas to reject them, in effect giving you much better control over where the cutting algorithm puts the seams.