To implement a 3D CG element into a photograph requires a lot of planning. It is important to mimic as best as possible the lighting and angle of the photograph, on the 3D model, therefore you want these elements to be as controlled and well documented as possible.
When taking your location photo it is best to record measurements of any elements of the environment you believe your CG element will be interacting with including its shadow. This will allow you to accurately model the scenes elements so that the CG element is able to believably interact with them.
A mirror ball also makes the lighting process a lot simpler to achieve. By taking a photo of a reflective ball which is reflecting the surrounding area, you are able to capture all the lighting information in one shot. This can then be unwrapped, and used as a surface in Maya with the assistance of Image Based Lighting to create a rough lighting setup that can be tweaked with additional lights.
Rendering passes can be used to allow you more control when editing the photo within software such as Photoshop. Beyond this other techniques such as colour correction or blurs within Photoshop