When you take a forced perspective it’s best to have the foreground and background look like they are together and interacting. This can be a problem when you have a shallow depth of field so you’ll want to maximize the depth of field by using a small aperture and using a wide angle. The wide angle is also helpful for exaggerating perspective. However, the small apertures often slow the shutter speed down to much to take a sharp photo, so on all but the sunniest of days you may need to increase the ISO (if you use Auto ISO, it should do it for you). Another way to increase the believability of the interaction between subject and scenery is to remove from the composition (in camera or by cropping later) items that make the interaction too improbable. For example, if where the subject is standing in front of fence and the scenery was behind it, it would be recommended to try cropping the area where the fence resides. A final trick before I leave you with summary, if the subject is supposedly exerting force against the scenery, consider tilting the camera to help convey that movement.