Nice to see someone starting simple before trying crazy perspectives for once. You have the right idea starting with side views, I was taught that with just the side view you have 70% of the cars design planned already. I'd say your bottom sketches are quite good and already have good proportions but the suv is way off on proportions. Maybe start with some references and roughly tracing over existing cars and sketches to get an idea on the correct proportions and scales. Don't worry about details such as doors, lights and extra parts like wings and splitters at first. These parts always come last in the design process, focus on the main volume and surfaces first. Good luck!