Taken from two separate articles on black and white thinking.

1. Accept that you’re not perfect. You’re human – you make mistakes, you’re fallible, you’re imperfect, and you’re vulnerable. Believing that we can achieve what’s not achievable – perfection - helps us to accept that we’re unfinished. We may be accomplished, brilliant, and unique, but we’ll never arrive at the destination we’re trying to reach when the standard we’ve set for ourselves is perfection.
2. The next time you feel judgmental, stop and ask why. Is it because you’re expecting too much of others? Maybe your expectations of your own perfection are being placed on others. Aren’t other people entitled to be just as human as you are?
3. Try to find the gray in one situation today. Things can be both good and bad, and people can be both capable and incomplete, self-confident and self-effacing, talented and average, and extraordinary and no more special than anyone else. Take the time to realize that we’re all in this together as humans.

Open your mind to new ideas. While of course it makes sense to think of whatever situation you're face with using an open mind, it's also important to keep your mind open at all times, not just when you're looking at a specific situation. Keeping an open mind can help you to think about the world differently, which will allow you to approach any situation (even the one you're looking at through an all-or-nothing lens) with new eyes. When you remain open-minded, you're likely to perceive a situation as it is rather than how you think it should be. New ideas are always useful and it's especially important to be open to them when you're trying to stop seeing the world in black and white.

Let go of your expectations. Personally I find that expectations are one of the main reasons all-or-nothing thinking happens to me. I think something "should" be a certain way, so I am either eager to accept the situation as normal when it happens as I thought it should or I am quickly disappointed when the situation doesn't meet my expectations. Letting go of expectations is one of the keys to ridding your mind of all-or-nothing thoughts. Expectations -- those little "should" and "should nots" in your mind -- can really force you into thinking in extremes. Letting go of the notions of how you think the world should or shouldn't be will really help those black and white thoughts to turn to shades of gray.

Look for the gray areas. While it's tempting, as I said, to fall into the "black" or "white" mentality, keep in mind that there are almost always gray areas. In almost everything situation, there are different layers and different ways of looking at whatever you may be faced with. It's easy to slip into that "black or white" thinking because it comes so readily to most of us. However, it's worth it to give any situation you see in black or white a little more thought to see what's truly happening rather than accepting your initial reaction.

Try to see things as they are. Much as I hate to admit it, I tend to see things the way I want to see them rather than the way they really are and this can be a major problem. It's often this distorted thinking that causes me to see the "black" or "white" in a situation because I'm taking what I see and transforming it in my mind. When you actually look at situation as it is, you're much more likely to see the layers and complexity of it. You're much more likely to avoid extreme thinking if you do what you can to remove yourself emotionally from a situation and really look at what's actually happening.

Avoid labeling with a single word. This one sounds simple, but it's important. When you think of something in terms of one word, you're limiting it immediately. Think about it like this... If someone asks how your day is, you usually respond with words like "Good!" or "Terrible." And even phrases, like "It was okay...", can be limiting. When you label a situation/person/etc. with a single word or phrase, you're instantly limiting it. Recognizing that everyday is more than "good" or "bad" is a great way to start realizing that situations are always more complex than a single descriptive phrase. Open yourself up to describing things in detail (at least in your mind) to avoid those thoughts in black and white.