When using a wide angle lens, it is very common for there to be a barreling effect on the image, where lines that should be straight have a rounder appearance. There is a simple way of counteracting this in photoshop.
Simply go to the ‘Filter’ tab and select ‘Lens Correction’.
Then select ‘Custom’, you can now slide the distortion bar over to the right to reduce the level of image distortion in your photograph.
Clone Tool/Healing Brush
If there is a certain part of your image that you do not want to be there, for instance, the barbed wire on the fence in the photograph below, you can get rid of it by using a selection of tools.
First is the Clone Brush, by selecting another part of your image you can then paint over what you wish to hide, replacing it with the part of the image you selected
Second is the Healing Brush, This works similarly to the Clone Brush but instead of you selecting part of the image, it does this for you. Simply paint over the part that you wish to hide and the brush will blend the area in with the surrounding colour and textures, masking it pretty well. you may want to use to clone tool to add more texture to the hide area after using the Healing Brush as this sometimes creates a smooth and unrealistic look to it.
I also used the same techniques to hide the string on this image of a watch