When editing a photo, it is important that everything is done in the right order.
This is not a concrete rule, but here is the suggested order of operations for retouching a photo with Adobe Photoshop.
Straighten
Crop
Levels
Curves
Saturation
Remove Blemishes
Select the Crop Tool in your Toolbox.
In the menu, select the Straighten Tool. (looks like a carpenter level)
Take the tool to your image and find a reference point of something that should be straight, like the horizon line.
Click the mouse, hold while drawing a line that follows a straight line on your photo.
Double click inside your crop or click the checkmark to commit.
2nd OPTION: With the crop tool selected, if you click outside the crop selection, you can rotate the image freely and adjust your crop.
Double click inside your crop or click the checkmark to commit.
Crop images for Better Composition
Often, your photographs end up with a lot of information that you may not want.
Look for the Crop Tool in your toolbox
If possible, don’t stray from standard photo shapes and sizes.
Preset sizes can be found in the menu.
Use the Rule of Thirds grid to place important elements of the photograph along the lines, or at the intersections of the lines.
When you adjust Levels, you're adjusting the mix of Shadows, Highlights, and Mid-tones.
Click the Levels Adjustment Icon.
You’ll see a histogram; look for three arrows in a line.
The arrow on the far left will make your image darker if you move it to the right.
The arrow on the far right will lighten your image if you move it to the left.
The middle arrow changes the mid-tones, which helps with the image’s shadows.
For most pictures, it's best to move the outside arrows to the bottom of the "mountains" and leave the middle one alone.
You can also adjust each individual Channel (Red, Green and Blue) by selecting them in the drop down menu for more advanced control.
The Curves tool is similar to levels, but it gives you more power to control shadows, highlights, and mid-tones separately.
Click on the Curves Adjustment Icon.
Typically one increases contrast by creating a slight S-Curve. The amounts will vary depending on the picture and the results you want to achieve.
Click and Drag down on the lower part of the line to deepen your shadows.
Click and Drag up on the upper part of the line to improve image contrast.
You can also adjust each individual Channel (R, G and B) by selecting them in the drop down menu. This is useful if your picture has too much of one color.
There will be times when you may want to adjust the colors in an image. (color intensity or even change colors for artistic effect.)
The Saturation Slider increases or decreases the vibrancy of colors.
The Hue Slider changes all of the colors in the image at the same time.
You can adjust individual colors by selecting them in the Master Menu.
Try selecting the click and drag icon (see on right) to adjust individual colors in your photo.
Click & Drag will adjust Saturation
CTRL + Click & Drag will adjust Hue
Blemishes not only include blemishes in the form of skin imperfections on people, but also include camera dust, and any other small marks or flaws.
Create a New Layer above your picture and do all your fixes on this layer. (set your tools to "Sample All Layers" - See Touch Up Note)
Use the Healing Brushes, Patch Tool as well as the Clone Stamp Tool.