Not getting the horizon level
There’s really no excuse these days! Nikon’s built-in Virtual Horizon option can help you get plumb-straight seas, landscapes and architecture. If your camera lacks this feature, activate the grid display instead – some SLRs enable you to do this in the viewfinder as well as on the Live View screen. If your SLR lacks both of these, use the AF points in the viewfinder to line up the feature you want to appear straight.
You can, of course, correct a sloping horizon in Photoshop, but this can lead to a significant portion of the image being trimmed off when the correction is made. It only takes a few seconds to get it right in-camera, so you may as well save yourself some pain later.
If you find the Virtual Horizon or grid overlay difficult to see on the rear screen, fit a traditional hot-shoe bubble level instead