I'm a pilot and have belonged to several flying clubs with grass runways. They all say that around 2/3rds grass, 1/3rd clover is the way ahead for a really hardworking surface (and trust me, the touchdown point of our main grass runway in winter, REALLY has to work hard. ) I believe that a proportion of rye grass is also common. I think that similar advice is common for playing fields - and advice online for what, say, to grow on your football pitch might be the best place to look.