Adjust colour balance automatically.

To adjust the colours in an image automatically, Select Image > adjustments > Auto Colour (Shift+Ctrl+B). It is always worth trying the auto function as very often it works a treat.

How to create a Sepia tone in seconds.

From the menu bar select Image > Adjustments > Hue & Saturation (Ctrl+U) and tick the Colourize box at the bottom right of the palette. For a sepia tone select a hue of about 25 and a saturation of 15. Any other tones can be selected with a tweak of the sliders.

Colour to mono with Channel Mixer

We can convert a colour picture to black and white via the Channel command via Image > Adjustments > Channel Mixer. Tick the Monochrome box and adjust the sliders until the numbers add up to about 100. This will give a standard B&W effect, but others are possible by varying the sliders.

Make your own colour palette

Click on the foreground colour square at the bottom of the toolbar and select the colour you require from the Colour Picker. You could use the colour sampler and sample a colour from an image too. Open the colour swatches palette and click the arrow at the top right of the palette. Select New Swatch from the drop down menu and you can name these batch of colours for future use.

Manipulating only one colour

Open the Hue & Saturation palette (shortcut Ctrl+U). We can select just one colour to change by clicking on Master and choosing the colour we want. If our colours isn't listed, click on any single colour in the list and then use the Eyedropper tools to select a colour directly from the picture. Move the sliders to adjust the Hue and Saturation accordingly.