Sensor Cleaning: A Clean sensor is very important in maintaining a high standard image. This document explains how to clean one.

Photoshop Playbook: Hundreds of Youtube videos are available to help you with common Photoshop problems. See here for an introduction.

Vanishing point: Cloning objects with noticeable perspective effects can be tricky. This video tutorial explains how to use Photoshop’s Vanishing Point tool to do it.

Photoshop Adjustment Layers: If you have cut part of your image to a new layer (Ctrl-J), you may want to adjust the tone, colour balance etc of that layer, and only that layer. One quick way is to bind the adjustment layer to the layer beneath it by creating a clipping mask. With the adjustment layer selected, all you need to do is Ctrl+Alt+G, or Layer > Create Clipping Mask or right-click on the adjustment layer and select Create Clipping Mask.

See also: https://helpx.adobe.com/photoshop/how-to/photoshop-layers-affected.html