Well, a pretty open ended question, but here are some random thoughts - I'm not a foliage expert but have done scenes with a lot of it:
1. Good source material. It really pays off here. Buy good assets or if creating them with specialized software do it right. There is a lot of cheap, badly mapped foliage around the internet: get the best stuff you can afford.
2. Think about Level of detail and distance from camera. Trees right near the camera or main focal point should be high poly with good textures and stuff further back and far away can be lower poly and resolution. This helps keep polygon count lower as well - see No. 3
3. Foliage can be expensive in render time and file sizes. Work efficiently and organized. Instance as much as possible. You'll need decent hardware to keep it rendering snappy.
4. I keep foliage on its own Layer or all in one Master null so I can hide it in viewport and keep my frame rates working well while working and tweaking the rest of the model or doing test renderings for architecture.
5. Leaves and grass have subtle translucency I. E. They show backlight from the sun. This helps realism but can add render time. If slowing down your scene, keep it turned off for testing and on for final outputs.
6. Forester is a decent plug in for Cinema with a big library and it can create materials automatically for a few different render engines. I use purchased models for the closest and Forester for the mid and far ranges.
I think Corona does very well with foliage. Hope that helps some.
e.
