I hate the white lines / window frame thing.
I think you need to focus on RENDER effects, like creating a transparent layer over the render, right-clicking the render layer thumbnail and going 'select pixels' (to select the render) and then painting that transparent layer in GREY... Then setting the transparent/grey layer to OVERLAY, then using the BURN/DODGE tools to darken the shadows (BURN) and SLIGHTLY brighten the surface that the light source hits (DODGE).
Another very easy way to get good-looking renders is using TOPAZ LABS plugins, specifically TOPAZ ADJUST (need to obtain illegally, pretty much). There's a ton of filters in there that can make a render POP or look more HD / HDR ish.
I also think u need to work on blending your renders with the background. This can be achieved by laying stocks over the render AND background, or maybe slightly masking/erasing the edges of the render... OR duplicating the render and then using a filter effect on the UNDERLYING render layer (like RIPPLE or GLASS or PIXELATE... All things found in the Filters menu) or maybe even just making the underlying render layer slightly bigger, and changing it's layer type to like colour dodge or something.... Or even STROKING the render or something with a gradient or solid colour, and setting the stroke to overlay/soft/light/color dodge/etc.
thats about it