Reality-checks allow you to determine if you are dreaming by performing tests that have different outcomes in dreams and reality. All lucid dreamers should make themselves familiar with at least a few techniques.
When to do reality-checks
Do it when you wake in the morning. It's common to dream that you've just woken up.
Do it if you encounter a dream-sign, i.e. something that regularly occurs in your dreams.
You should also get into the habit of performing them when something out-of-the-ordinary happens, e.g.:
Someone says something out of character or responds to you in an unexpected way.
You see something extraordinary or inexplicable.
You find yourself in an uncomfortable or embarrassing situation.
Some people perform them regularly throughout the day to increase their awareness.
How to do reality-checks
The following list includes the most commonly used and reliable tests. There are many more.
Look at your hands
You may have too many or too few fingers or your hands may look strange.
Read some text
Text will often be inconsistent or may be illegible. Read from a book, poster or anything else. Remember the text and look away. Now look back and read the text again.
Retrace your steps
Can you remember the sequence of events that led you here? If you can, do they seem plausible?
Use a light switch
The lights may not react to the switch as you would expect.
Look in a mirror
Your reflection may not appear as expected or may not mirror your movements. Maybe you will see someone behind you.
Just think about it
Take a moment to look around and think about your surroundings and situation. Experienced lucid dreamers will often find that raising their awareness is all they need to do.
Don't ask someone else if you are dreaming. Dream characters generally don't know they are part of a dream and will be adamant that you're awake.
Sometimes you may need to perform a few different reality-checks to be sure.
Don't rush it. Quickly glancing at your hands and then carrying on is not enough. Take your time and give the test your full attention.
Remember that lucid dreams can look and feel real. Don't assume it's too lifelike to be a dream.