UV editing can be very stressful. If you're feeling a bit tense, just choose Relax from the texture editor's Tools menu. Okay, what Relax actually does is adjust the proportions of selected polygons in UV space to resemble their proportions in 3D space. This can help remove distortions on selected sample points.
Relax works a little bit like a spring system, where the points are adjusted to fit the 3D polygon proportions. By default, a relax operation can affect all of the points in the selection. However, you can anchor the points on the selection's boundary so that they stay in position while the internal points are adjusted. This is especially useful if you want to relax a portion of a UV coordinate island without affecting the surrounding points.
Make a selection of sample points in the texture editor or in a 3D view.
In the texture editor, choose Tools 
Relax. The Relax property editor is displayed.
Adjust the Iterations to control the number of times that the relaxation is run.
More iterations usually yields a better result, but the higher the number, the slower the relax calculation.
Adjust the Increment value to add a "damping" factor. If the points tend to diverge instead of converging to a rest state, decreasing the increment can help.
Activate the Anchor Boundaries option to prevent the boundaries from moving as the selection's internal points are relaxed.
Except where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License