This article is a collection of advice for specific cases you might need a UV map for. This is based on my experience on working on characters, props and sets in our open movie projects.
There is not just one way to make a good UV map and it heavily depends on what you need it for. You could create a single UV map that can be used for all cases you need, but don't hold back on using multiple UV maps too!
So the article is divided into those use cases and what they need. Projection mapping and heavy procedural shaders and Geometry Nodes won't be covered here.
I'll also not go into step-by-step details. There are many tutorials out there that can show you how to unwrap UV maps and use features that are mentioned here.
The primary goal here is to reduce the amount of area and angle stretching as much as possible. So it's generally better to place more seams rather than less. Depending on how well the seams are placed you can of course get away with less.
Use the 'Area' and 'Angle' stretching overlays in the UV editor to better visualize this as a heat map. Once any angle turns past green, it's probably good to tweak it. The area stretching color just needs to be roughly the same everywhere for consistent resolution.
UV seam placement highly depends on your intend to paint in 3D or 2D. In 3D there is less to worry about since seams can be easily painted over. But when using the Image Editor or external image editing software like Krita, keep in mind that it will be difficult to paint over seams and not make this very visible in 3D.
Since 3D painting tools have become increasingly advanced and common to use over the years, seam placement has become less of an issue. So it's generally better to place more seams rather than less. Stretching and uneven texel density is much more of an issue than what seams might cause.
The 'Live Unwrap' feature can save a lot of time and provide real-time feedback. By pinning UV points and moving them, everything that isn't pinned will be unwrapped live. It can make aligning, straightening and defining a flow of the UV map much easier and intuitive.
This is a separate setting for the UV Editor and the 3D View. Keep in mind that this setting is saved in the Scene and not the Object. So be sure to disable it once you don't use it! It also tends to break when any UVs are flipped or twisted.
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An example of using Live Unwrap on a clothing top to resolve stretching and straighten boundaries.
Symmetrical UV maps can be useful to make UVs easily recognizable. A logical arrangement makes them fast to parse and identify. It also allows areas to be mirrored over in 2D image editing.
Fully symmetrical body UVs across multiple UDIMs with the mirror modiifer. The "Modified Edges" overlay is used to display generated UVs.
