Use some keyword suggestion tools to find them. But maybe every keyword you selected is very hot. So work hard and struggle to rank in the first page.
Go to DPs suggestion tool and look up some keywords related to buying cars that get around 50-100 searches a day, optimize for them instead of the big ones
All of the keywords are impossible to get ranked on. It's all "buying cars" "car donation" HUGE competition.
Make different pages for different keywords and the urls of the other pages should be like this: keyword-keyword.html also the anchor text for the link must be keyword keyword