"The armored cars of dreams / contrived to let us do so many a dangerous thing ..." - Sleeping Standing Up, Elizabeth Bishop
Whatever you do, ask yourself: "Am I dreaming?"
For the best and quickest results, do it many times during the day. As well as repeating this often, it's helpful to really think about what you're saying and ponder the answer. Not dreaming? No. But why not? How can you tell?
In dreams, the world is often morphing. People and settings are regularly inconsistent. Think about the people around you. Are they behaving in a typical, consistent manner? If the guy behind the counter is a wizard strumming a cat, you're probably dreaming.
Check out the air, the light. What can you hear? What are you wearing? Naked in class again? This had better be a dream.
Reminders are good. You can try a Smartphone app that chimes at regular or irregular times during the day. PING! Perform reality check. A meditation app can perform the same function, but rather than noticing the tension in your shoulders, you can do your reality check. And relax too.
Another handy reminder is to write "AM I DREAMING?" on a card and keep it in your handbag, purse or wallet. Every time you flip them open, you have your reminder to see if you're dreaming or not. You could stick this on your phone case, since your mobile phone is probably something that you have with you all the time and look at regularly. Likewise, a reality-checker is well-placed as a screensaver, home screen or lock screen on your phone or computer.
Live alone? Write it on your bathroom mirror or Post-it notes around your space.
One of the benefits of frequent reality checking is an increased awareness of ... well, everything. It's a kind of meditation. Taking time to see, feel, hear, smell and taste the world promotes a feeling of well-being that is not just good for hippies. It can be good for everyone - particularly in the fast-paced Western-world from which I write - to take a momentary time out and really observe, really feel, really exist.
As well as observing your environment, actively testing reality is a positive, effective way of improving your ability to lucid dream.
The 'Am I Dreaming' card is particularly useful for reality-checking, because text is notoriously difficult to read in dreams. Either it tends not to make sense or it moves. Read, look away and look back and it will often be different.
Other common reality checks that involve assertive testing include attempting to push your finger through your hand or sticking your hand through a solid object. You guessed it: if your finger goes through your hand, you're dreaming. If you knock over half the wine bottles in the beverages aisle, get the hell out of there - you're about to be asked to pay for the damage.
Turning lights on and off is said to be a good one, though I've not tried this in dreams. Lights rarely behave the way they should apparently.
You could also cut to the chase and try to fly. Go on. See if you can fly right now.
Top tip: start on the ground floor.