A couple things I like to keep in mind:
First of all, while most of us like to go for a "natural" look, understand that aquariums are by definition unnatural environments. The water in most FW environments is murky, either with suspended substrate and/or algae. Lighting is typically dim, and you only find rooted plant growth at the very edges. Fish in general don't like to be exposed in brightly lit, clear water, but that's how we like to look at them. So don't obsess too hard about recreating an authentic slice of the biotope--create an environment that's esthetically pleasing to you while keeping your fish happy.
Also, some of the links make reference to the "golden ratio." The essential point is that you are looking for balance, as opposed to symmetry. Symmetry and straight lines are unnatural-looking; balance is pleasing.
I like to work on the illusion that structures continue outside the limits of the tank. In particular, I like objects on the tank floor that give the illusion of something buried which is peeking out of the sand. I have some pots and crockery pieces that I cut with a tile saw so that they look like most of the item is buried. You can achieve the same effect by finding rocks that are shaped like pyramids--the shallower, the better. If you set these into your substrate, you create a "tip of the iceberg" effect.
You can do the same thing with driftwood by slicing it at an angle and sticking the cut edge to your tank floor, so that it gives the appearance of a dead log buried beneath the sand.
If you like the look of fish swimming through root tangles, you can create the illusion of mangrove-like roots by turning branchy pieces of wood upside-down. I'm always scanning roadside brush piles for likely pieces (bleach, soak, boil, pressure-wash, leave out in the weather for months, etc)--crape myrtle is one of my faves for this effect.
Stay away from pitchy woods like conifers, which will reveal themselves at first boil by gunking up your pot.