|Shape Originated with a simple cube|
1. Box Modeling - In nearly every instance its possible to start with a plane or cube to model a sphere or cylinder. Using the subdivision surface modifier to shape the cube, followed by object mode convert to mesh (alt C) nicely shapes a whole or part of a model, so that you keep your lo poly start, and your quads for less frustrating unwrapping and texturing.
2. To straighten a group of face edges, use the combination (Key S), (Key X or Y or Z) depending on the edge direction, and (Key 0).
3. Draw loop cuts close the edges of ornery holes, door or windows opening made with insets or deleting faces from spheres. Much like you would do when you sew in a patch to a hole in your sock, you need to ease the patch into the hole. Loop cuts do it automatically. Use reason. Loop cuts do add a few faces, but it well worth.
4. Check your normals (whether the face is facing in an interior or exterior direction) by using (Mesh, Normals, Recalculate Outside) after you box model, draw your loop cuts, and straighten your edges. 9 out of 10 times, there won't be a problem, because you avoided the issues in the first place.
Coming next how to avoid unwrapping quagmires.