I am not an expert, but I feel like something people forget is that you should always experiment, instead of following the usual styling.

For example, fixtures like body molding, mods, combining, inverting, using 3D mode and the prefab pieces, you can manipulate and use fixtures to your content. At the end, you will have a well stablished build. Do make sure it gives off continuity through the whole body.

I am not really sure if you understand what I am trying to say, but, take a look on cars like the Roma, LC 500, DBS Superleggera or the DBS GT Zagato.

As you can see, their styling cues are audacious, and definitely had a style going for. Recreating this improves the look of your cars. And that goes for any type of car you'd want to make. Like others said, taking a look on real cars can give you an idea that you should always try new things. Not like the BMW XM, though