Katt,
Very nice work for a beginner. You have received plenty of rendering suggestions so I will tailor mine to Interiors based feedback. There are two levels of design that I always look for in good imaging that set the really great project work apart. One is scale, and the other is assembly. And they can apply across multiple aspects as well.
For instance - Look at your two images and then look at similar spaces in magazines and/or on the web, or at actual life. If your environment doesn't look like what you are rendering, that doesn't really matter. What you are looking at is in the details of scale and assembly.
For instance in the first image;
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Look more closely ta how a window that size would be detailed. The small section of wall (assuming drywall covered) below the window to the floor is a bit odd from a construction assembly standpoint. It would be more likely the internal opening would go to the floor and the frame would sit on the floor. Or as an alternative put a nice thick sill/window stool on there wher you could set plants in the sunlight.
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The Shelf over the flat screen - how is that attached / supported from the wall?And as was suggested before - a slight bevel on the edges reflects more realistically - just like adding small gaps between the shelf and the wall would add a slight shadow line hinting at an attachment.[/[/list]
For the second (kitchen cabinets) image;
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Look at real life and then the scale of minor details like the thickness of the counter, the height and depth of the toe-kick (base) of the cabinets, the support structure (plate or platform) that would be at the top of the peninsula leg under the counter, and ssuming granite as the material you are depicting - what type of edge the surface would have.
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Small details like a little tilt / offset of the painting on the wall, some definition on the material and what is in the opening in the base cabinet at the corner, the material definition (needs to contrast) of the handles / pulls
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The scale / size / materials of the Range / Exhaust hood / backsplash
It not difficult to tweak these things to make what is a very good image even more realistic, it just takes knowing what to look for and the effort to look!
Looking forward to seeing your updates!