Many people struggle with SEO for one simple reason... They try to optimize for extremely generic, high volume, popular keywords - like car. This is never going to work. Those words are already owned by companies with marketing budgets that represent the GDP of small countries.
To be successful, you need to focus on long tail, niche keywords related to your product or service. As an example - cars for people with bad credit.
I've seen long tail keywords work wonders in SEO for small businesses. They also have proven to convert better.
For more information, here is an article : Long Tail Keywords : Using niche keywords to get the traffic most businesses miss.