Bonus: Seam Painting
This bonus video goes into seam painting in Blender. Though not a necessary step, seam painting helps hide the seams otherwise generated when a mesh is unwrapped. Basically it gives you contril over how the mesh is unwrapped. This can make texture painting and other steps that come later much easier.
This video is a bonus video added as part of a larger playlist on making Unity, VTT, TaleSpire ready meshes in Blender. The larger playlist series goes step by step into breaking down a high poly mesh meant for 3D printing into a low poly mesh with textures that is appropriate for Unity / TaleSpire / TaleWeaver.