OOoo I hate personal statements and cover letters. I'd say sell yourself as much as you can without appearing arrogant or talking about abilities/achievements you cannnot support (i.e., although embellishing on the truth seems common practice these days).
I was watching an interview on TV featuring the new 'Carol' from Countdown. When she applied for the Countdown job, the first line of her personal statement read 'I'm from the top shelf'. IMO, this is type of approach is arrogant...though she got the job, so who knows...