1a) Just start making videos: Yeah, it sounds simple, but getting started is the thing that is the hardest. You may have watched hundreds of car videos online and think you videos won't measure up. Guess what? Your videos are fine because they are your start. You can get better at filming and editing as you go. Just put up the best content you can for now and keep going.
1b) Keep a camera on you at all times and be ready to film: You never know when supercar awesomeness will occur. Be ready to capture the moment.
1c) Figure out where the cool cars are. Go there. Film. Repeat. (This one should be self explanatory (^_^) )
2) Explore the videos of top supercar channels and see what they do well: Notice how these people use tagging, links with social networks, and other tactics to drive traffic to their videos. Think about what these people are doing that you can do too.
3) Do NOT be discouraged: There will be naysayers both in real life and online during the entire time you have an online car channel. Why? Simple, some people just love to hate. Learn to separate the baseless hateful comments from the comments which, while possibly being a bit hard to hear, contain valid points about areas in which you can improve.