UV mapping is a whole art form in its own right. There are basically two methods - projection and unwrapping. Projection is a quick method which only gives good results on simple geometric shapes which resemble the 3 types - cube, cylinder and sphere. Anything organic needs to be unwrapped using seams and pins. Unless you assign temporary shading domains to each flat part of the mesh and do a planar map for each.
Basically, to unwrap, you look at the mesh and decide how you would cut it up if you were making a paper pattern to lay out flat. Then you make seams along the edge loops which represent how you would cut it up, add pins in appropriate places which serve as a fixed point around which the UV map flattens out symmetrically.
If you would like to post the mesh on a file sharing site and PM me the link, I’ll try to show you a step-by-step:)