Okay, lets help you improve
First of all, when cutting out images, boost the tolerance of the magic wand, you don't really want that white outline around the renders unless you are using a white backgruond - in which case you usually cant see it.
Secondly, use renders/backgrounds that match, or blend them together. This can take a while to master, but practice is always good

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Thirdly, try to make your text stand out less, use a variety of fonts. The font you have used on most of these sigs is okay, but they get a bit same-y after looking at all of them together.
Finally, use a variety of renders, try not to use the same one twice unless you are simply improving your peice.
Of course, I critisize thinking someone has Photoshop. Which, you dont, so you may not be able to do all I have suggested, due to less features.