To create the appearance of a river or stream, it is best to imagine you are standing in the middle of the river/stream and looking toward the bank. So the very front along the glass can be left as substrate (fine gravel, sand). Plants at the back can be larger/taller, as if growing on the bank at the water's edge. Remembering that tropical rivers/streams flood for half the year, you can imagine that we are at the high water point in the year so the water has risen and the tall plants are those that would otherwise be emersed. Smaller plants can be spaced in front, keeping the area along the front glass mainly open.
Bogwood should be placed lengthwise from left to right, as it would naturally occur in a river/stream. Close to the back, some vertical pieces will give the impression of standing trees that are now submerged (wholly or partly, depending upon tank depth and length of the wood). Moss attached to such pieces will add to the perception. You can get one impression of this approach in my 115g Amazon tank photos.
Some small streams in Amazon basin are thick with branches, twigs, roots. Dry leaves litter the substrate. The Rio Nanay in Peru comes to mind, and other similar Peruvian Amazon streams and creeks. I have sort of headed in this direction in my 33g lagoon tank, though I had to stay with bogwood chunks since I haven't been able to find true branches in local stores. I will need to do some hunting in the forest for oak and beech branches. But the overall intent is shown in this tank's photo.
Some streams have rock, some do not, so that is up to you. If it does, then rounded river rock in varying sizes works best, replicating boulders worn down by the flow of water. These can be placed intermittently, or grouped; try to use rocks of the same type, at least in a grouping, for a more natural look. Flat chunks of rock such as basalt meant to form ledges is another use of rock. I use a bit of this at the left side of my 115g.
If rocks are used, the chunks of bogwood look natural if placed as if wedged by the current among the boulders. I aimed for this perception in my 90g river habitat, though the increase in plant growth has mostly hidden the hardscape design.
Hope this gives you some ideas to work with.