My first try at CG nature. I need help. Any advice on how to model realistic nature is welcome! I haven’t bought a membership to “The Nature Academy”, but I’d like to.
BI or cycles?
Grass is a bit too uniform length. Are you using hair or object emitters? I’d suggest turning up the random on length.
Some different types of sparser, taller grasses would probably help break up the monotony.
Your grass is very, incredibly green. A bit like astroturf. 
If you are in BI, use a blend with ramp texture to vary the color of the grass blades - black at the root, darker green in the lower middle, greener in the middle, a bit of brownish/tan near the tips - and vary to taste. If in cycles… I’m not entirely sure, actually. I haven’t figured out a great way to do grass in cycles without the ramp feature, been meaning to dig into that but haven’t yet.