For the forced perspective to be effective you want the subject (your model) and the background to be in focus. A blurred background looks cool in 1:1 subjects but in scale models can bring out the "toynes" (I just invented the term!) of it.
You need a high f/stop (11 or more) to get the effect. Of course natural light is a must in this situation. You could combine the setup with artificial light to manipulate the shadows but that is another argument all by itself. Shoot a a low angle, like you were a scale little guy standing next to it. A cheap way is using a "cheap" camera like a cell phone. Due to the nature of it and its little lens, when you shoot in Auto in these conditions the cell camera almost always chooses to get everything in focus due to its limitations. Micheal Paul Smith uses a relative cheap camera and at one time tried a higher end camera but it produced images with too much detail making the models look toyish so he went back to his older equipment.
Here is a few Ive tried. The model is 1/24, I shot it at a f/22 stop in very bright light. It blurs some details and makes the pic to look more like a random snapshot of a cool subject.
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IMG_3891-Edit-Edit by nenekinkin, on Flickr
The model is on a folding table that looks like some kind of pavement. Tried to line it up with the background. I shoot this handheld but a tripod would have been better. When you got to such a high f/stop sometimes you would need slow shutter speeds and motion could make you image blurred if handheld. This depends of course in the lighting conditions at the time. If the light was very bright and harsh ( like in my example) the camera could be handheld die to the vast amount of available light.
To this one I added some effects to make it look like an old photograph in the same time frame of the car itself. Maybe a enthusiastic guy that jusy bought his first cool car and took a pic with his Dad's film camera...Of course is photshopped but IMO, you can get creative and must important, enjoy what your doing, have fun! Life is too short...
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IMG_0805-Edit-Edit by nenekinkin, on Flickr
Excuse me if a bored you to death!! LOL! I just love photography!