How to groom hair without getting wobbly results
First, make sure the fibers dont have any natural curliness to them.
I would start by reviewing the documentation for the Fibermesh modifiers. Then open Tool> Fibermesh > Lightbox, and try out some of the different fibermesh presets there. Look at the result the different fiber settings have. Then load one of the curly hair styles, and try to straighten it. You’ll want to do this by setting any twist or rotational features to zero. Notice that many settings have a second “Variations” slider that randomizes the results. Make sure these are all set to zero as well.
Once you have perfectly straight hair, accept the fibermesh results, and use the basic Groom brush to comb out the fibers. The Groom brushes work best when you use them like a comb–long sweeping motions along a gentle curve. If you take a comb and simply use it to agitate a small section of hair it doesn’t work as well.
Results may vary with the type of Groom brush you are using, and its individual settings. Make certain features like Stroke> Stroke Jitter and Brush imperfections are off for any brushes being used.
If making especially short hair, consider limiting the number of Segments per fiber. The fewer segments there are, the fewer opportunities for the points to fly in different directions, and the smoother the curve it will make.
The Smooth function can also be used to smooth out the hair, though this may result in a loss of volume as well.
If this doesn’t help, we may need to look more closely at the context of your screenshot, and the situation the fibers are being used in.