Let's start with my six brainstorming ideas about what to write in your Summary section. You don't have to cover all of them — you can just pick the ones that show off your very best stuff. Or, you might be able to combine some. (For example, the first and second points often work well together.) Here you go...
Indicate your career objective.
State how much relevant experience you have.
Summarize your qualifications for your job objective.
Talk about a highly relevant or an overall career achievement you're proud of.
Give a brief sense of your work or management style.
Refer to a personal trait that supports your job objective.