Always use a checker pattern to verify your UV islands are properly flattened.
<aside> ℹ️ A little bit of distortion is OK!
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Your final UV pack should have a uniform checker size for all visible surfaces.
Hide texture seams in crevices, material transitions, gaps, and other natural seams.
Ring-like shapes can probably be mapped into a "strip." Strips are rectangular and therefore easier to pack with other UV islands. Which method you use is dependent on the context of your model but generally Method 1 (below) will have less distortion and allow more total UV area to be utilized.
Your modeling package should track the total amount of area your UVs occupy inside the 0-1 region of your UV editor. An ideal percentage is 80% or more. You should aim for a bare minimum of 70%.
<aside> ℹ️ This won't always be achievable, it just depends on the shape of the UVs.
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<aside> ℹ️ The more area you can cover, the more pixels from your texture map will display on your model. You generally want to avoid resorting to increasing the resolution of your textures, as this can cause some serious performance issues.
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Identical elements of your model can be duplicated and/or mirrored to allow them to share the same UV space, also known as UV stacking. Stacking frees up more space for all the other UVs which in turn increase the overall texel density on the model. In the image below, the two clips and their bolts are sharing UVs.
