Hello, welcome to the automation community, we’re very glad to have you 
If you’d like real time tips and tricks to improve your design, I highly reccomend you join the Automation Discord. There are plenty of people there happy to help you improve, and it’s a live chat, so we can help in real time.
If not, that’s fine too. I highly reccomend Titleguy1’s tutorial on design if you’re just starting out.
Fundamentally, you seem to have a good idea of what makes a modern design, I’d recommend you focus on the small details. Such as creating modern headlights., picking a grille that doesn’t feel so empty, or at least filling in the blank space with a badge.
Edit: I’d also recommend creating a company thread to post all your cars to. It also helps get you in the roleplaying tycoon mood.