There's various things you can try, but without having too much info on your campaigns, I'd say:-
try making your keywords more targeted rather than generalised. eg. rather than say "cars", say "used ford cars".
use negative keywords. eg, if you sell cars, then exclude phrases like "hire", "rent", "clean", "repair"
group your related keywords, and then create a custom ad with custom text for that keyword group. Also use the main keyword in the title.
check your target country/language settings.