If you need to quickly select an area of similar color such as replacing the sky or a green screen Magic Wand is your tool.
Magic wand works by selecting similar colors in your photo, so if you have a photo of a model in front of a solid color background you can use magic wand to automatically select and delete the entire background. Of course you might not always have the luxury to use a nice clean background so here are some tools to make your life easier.
Above is the first half of the magic wand menu. If one click is not enough to cover your entire selection you can use the add (or hold Shift while selecting), subtract (or hold Alt/Option while selecting), or create intersection(or hold Alt/Option + Shift while selecting) icons to help you expand and perfect your selections.
Tolerance value determined how much similar color Photoshop should pick up. If the object you are trying to select is fairly evenly toned you will only need to low Tolerance value to work, but if your background is poorly lit and has too much variation, you might want to go with a higher value. The only problem with setting high Tolerance is that you might end up selecting colors you do not need so it might be better to set the Tolerance low and use the Add/Subtract function.
Anti-Alias, it will make the edge of your selection a bit softer to create the illusion that the edge is smoother.
Contiguous selection will only select area that are connected. See the example below, I tried to select the white background with Contiguous on, it does not select the white background isolated by the pink heel and the black heel. If I turn contiguous off, it now selects the isolated area but also everything else that looks like the white background such as the highlight area on the heel.
Turning Contiguous off might save you a few click but you will also risk selecting areas you do not need, you are better off leaving Contiguous on and use the Add/subtract selecting technique discussed earlier.
By default Sample All layers is turned off, magic wand will only work off of the active layer, even though you can see the layer below magic wand will still ignore it. Once Sample All Layers is turned on, magic wand sample everything that is currently visible.
In addition to Tolerance, you can also change how much color magic wand will consider as similar by changing the Eyedropper sample size.
Select Eyedropper tool (I), under the option bar, choose a bigger sample size.
A 31×31 average means it will look at the closest 31×31 pixel area and use the average value of that entire area instead of sampling one color pixel. It will be useful if the object has a lot of tone/value variation.
You can refine the selection by expanding, contracting or softening the edge and even automatically retrace the edges using the Refine Edge Tool. It is available in most selection tool such as lasso or marquee, you can also find it under the Menu Select-Refine Edge or with shortcut Alt/Option+Ctrl/Command+R. Read my article about Refine Edge here.