It's not as much a matter of "removing" things as replacing their pixels with pixels that blend into what is around the object. For instance, if you want to remove a light pole and some wires, you will copy pixels from either side of the light pole on top of it with the clone tool in a way that blends with the background. For the wires, you'll do the same but likely with the sky if they cross the sky. This replacement process can range from very simple to extemely complex to virtually impossible.
Sometimes I'm shooting subjects that I know will require this kind of retouching and I use a trick that saves a lot of time. BTW, I tend to shoot in manual mode and it's important that the exposure doesn't change between shots. So here's a common situation-- I'm shooting an architectural layout of a commercial building that has wires and poles in front that I want to eliminate. Because I will want to replace the poles and wires with what is actually behind them on the front of the building, I need to take my shot, then move the camera horizontally (to remove vertical objects like poles) and vertically to remove horizontal items like wires. You want to keep the camera in the same plane (careful not to tilt the camera up/down or swing it left right) and take another shot. You generally don't have to move the camera much to reveal what was hiding behind the object, and you can also tolerate a small amount of change in the attitude of the camera. When you get the images into photoshop, it's a matter of cutting the revealed areas of the building in the second shot and layering them over the objects in the first shot, and blending the images together. This is done in layers, which also lets you use the transform tool to make slight corrections in perspective. It can be a bit time consuming, but you can do things with this technique that are almost impossible to correct with cloning alone, and is generally much faster than cloning, and I always get a kick out of clients when they are amazed to see their building without the ugly poles and wires.