What would you recommend for my lawn which is hungry and also needs greening up?
For a big lawn, the best thing is to use a slow-release lawn feed which lasts for 3 months usually and boosts the grass evenly throughout that time. These can be difficult to get but are available in some garden outlets.
Failing that, on a large lawn us agricuultural fertilis such as Cut Sward, but only in small amounts of 20g per square metre. It is cheap but gives a strong boost.