I was thinking there are some people who would like to know how to squeeze out every performance out of FS9 to make it look better and more realistic. It's really more up to the add-ons since there are not a lot of things that you can do to FS9 itself. No rocket science, just some small tips, nothing special.

NOTE - make sure your PC can handle FS9 at max settings

1. Locate and edit your FS9.cfg. Replace the values of this lines with the one bellow
TERRAIN_DEFAULT_RADIUS=9.500000
TERRAIN_EXTENDED_RADIUS=4.50000

2. Max out all FS9 settings except the Mip Maps, they should be set at 4

3.Install the following add-ons for better ground, airplane and environment details
- Ultimate Terrain Products
- Terrain Meshes
- Ground Environment Pro
- Real Environment Xtreme
- Real Environment Pro - it's a freeware add-on, I use it for the landing lights, runway textures (dry, wet or snowy), Tree Gen, 3D Environment and Environment Reflection (it will make the plane more reflective, pretty cool feature)
- 3D Lights Redux

4. Use ENB Series, this will add a cool effect and will definitely improve the look of the game

That's about everything you can do to FS9, if you know any other things feel free to reply.

Enjoy !