Split toning is about adding different tints to highlights and shadows, and can add a little something special to an image.  While easily done in Lightroom, you can get a little more control over the process and outcome if you do it in Photoshop. This video by Eye Stocker showcases a very easy method using “solid color” adjustment layers and “blend if”:

[REWIND:] SPLIT TONING | THE ‘SECRET’ IN THE RECIPES FOR MANY ADORED IMAGES, & TOTALLY UNDERVALUED

Here’s how it works:

Bring the photo you’re editing into Photoshopand then make a new “solid color” adjustment layer. Select a cool shade for the color, and rename the layer “shadows.”

Here is the starting point for this process – there is no split toning applied yet.

Set the blend mode to “soft light,” and you will see the whole image has taken on tones of the color you selected. As you may have guessed by the name given to the layer, however, we don’t want that color everywhere. We only want it in the shadows.

The shadows have been toned blue in this photo.

Double click on the layer, or right click and select “blending options” from the menu that pops up, and notice the “Blend If” sliders at the bottom of the panel.

Using the bottom slider labeled “underlying layer”, drag the highlights slider points at the end of the slider to the left until the cool tone is only in the shadows. It’ll look choppy – to fix that, option-click the slider and it will split in half. Drag the left half back toward the shadows side of the slider until the transition looks smooth.

Now that you’ve set up the tone for your shadows, do it again for the highlights.

Here, the highlights have been toned a shade of orange and the blue shadows layer is disabled.

Make another ‘solid color adjustment layer’ set the blend mode to “soft light,” and rename to “highlights.” Turn off the shadow layer so you see clearly what you’re doing on the highlights layer and do the reverse of what you just did for the shadows – pull from the far left slider to the right until only highlights are affected, then split the slider and move the right half until it’s smooth.

Shadows and highlights are toned and set to 100% opacity – the effect is a little much.

Create a group for the layers called “grading,” and adjust the group’s opacity to taste.

Now that you know how it’s done, you can play around with all the settings – vary opacity on different layers, try out different colors, and just have fun with it until you find a style you like.

Here is the final image, with split toning applied the “grading” group’s opacity reduced to around 40%.