I think the reason for the diminished number of replies is obvious: you are attempting to perform tasks that stand outside your current level of skills and knowledge. The composites you are trying to create are intermediate level graphics, meaning they require strong skills and knowledge in the following areas.
1. Perspective - perspective is highly important in the world of composites. Correct use of perspective in every element serves to help give off the impression that all of these elements belong in the scene.
2. Lighting - lighting is the key to compositing, and not only makes selections easier, but also makes the composite look real. You can learn all of the selection tricks and Photoshop effects you want, but if the lighting on your subject versus the lighting in the environment in which you place them is different, it’ll never really look real.
3. Color application - knowing how to apply the various colors to a scene. Knowledge of how to place colors that either compliment the warmth or coolness of the scene or contrast each other to provide greater impact for the person viewing the final work. Color also gives everything in the scene a common theme.
4. Rule of thirds - rule of thirds encourages use of placement of objects or key elements in a scene to create more tension, energy and interest in the composition than simply centering the subject. To use this rule effectively, an image should be imagined as divided into nine equal parts by two equally-spaced horizontal lines and two equally-spaced vertical lines, and that important compositional elements should be placed somewhere along these lines or near their intersections.http://en.wikipedia.org/wiki/Rule_of_thirds#cite_note-2
My suggestion here is for you to take on smaller tasks or projects that get you more familiar with the four items I listed above. Once you are comfortable with these skills, then you can move on to more intermediate skill projects.
Just my two cents, for whatever it is really worth.
