I don't know if you understand if I reply in English, but I hope that maybe the google translator helps.
I would like to help and give you tips, perhaps others feel like they should share some advice, too. With your image, I am not sure where to start, to be honest. So the following is in no particular order:
- You should use the setting called Ray trace objects. In order for Ray Trace Objects to make any sense, the Anti Aliasing value needs to be at least at 3, but for anything photo real, you need to at least use AA 6. This is not a rule that applies all the time, but I think it is a good guiding value. You render looks like you had AA at 1 or 2.
- The tree models that you use are not good. Huge trunks, and a peculiar canopy, it just doesn't add up. At Xfrog, they have some good looking models, particular from the Europe 3 collection. You could also try Walli's tree from Silva3d, or nwdanet.com. There are some free ones, too, if you don't want to spend anything on the tree models. Try Xfrog's site for some free models. Also, try to vary the size of the objects that the use in populations.
- You have got a road, that's a start. I think it needs some more detail to look like an actual road.
- I think your biggest opportunities for improvement lie in both the selection of natural color, and the use of realistic lighting. You can get really good results without studying the theory, if you had a photograph as a guideline, and attempt to exactly copy the colors and nuances from that photograph, and the lighting, too. If you follow only one of my several suggestions, then do this particular one: get the colors and the lighting exactly like in a reference photo.
- I don't know if you have the free edition, or the proper TG2 Deep edition. If you still have the free edition, I advise you to upgrade, but if you can't, you should perhaps try a scene that doesn't require lots of populations. In a forest scene, you would expect all sorts of plants to show through, so that's hard if you only have the free edition in combination with no access to a variety of models. With the free edition, you may still get some variety going on in your image, if you hand-place individual models in the foreground and mid ground at least.
Regards and good luck!