Theoretically you can get rid of all stretching - by making every edge a seam . But that’s not useful at all and in reality you’ll always face some areas that have stretching.
Now there are a couple of technical things that might cause problems. For starters, in Object Mode, press Ctrl+A and select Scale and Rotation to Obdata. This applies all transformations you might have made. Otherwise, the UV editor doesn’t take note of those transformations and maps everything like it originally looked. Nasty.
Secondly, there are two methods for unwrapping. If you go to Editing (F9) -> UV Calculation (next to Multires), you can choose between Conformal and Angle Based. They unwrap stuff a bit differently, with one being better for organic models and the other for mechanical models. Just try out the other if something really wonky is happening.
Of course it’s likely that you still haven’t grasped the concept yet. Like all aspects of 3D, it’ll come with practice. Why don’t you attach a .blend file so we can try to help you out a bit ?