The stem lengths in the background seem inconsistent-- it's like having split ends in your hair cut. Try to train them into more natural looking shapes. Overall though, the placement of plants in fore, middle and backgrounds is good.
The wood positioning is unbalanced, and it's placement makes it too strong. It also would be better if the whole branch were not covered with moss, and if the moss were trained better.
The fish may be too small. I'd try to get an additional school of slightly larger tetras.
Over all though, it's pretty good!