Below are some guidelines and suggestions for the use of visualization and affirmations.
Phrase affirmations using the first person singular.  Take ownership of the statement.  You can not control others only yourself.  For example, “I am...”, “I can...”
Phrase affirmations in the present tense when possible.  You can not change the past.  The future is too unpredictable to control.

Phrase affirmations in the most positive way possible.  Avoid the use of words like “no”, “don’t”, and “not” in your affirmations.  This is very important because your brain is not capable of visualizing a negative
action.  The right side of your brain is predominately visual, the left side is logical and literal.  In many ways they do not communicate very well.  If you are practicing self-hypnosis all suggestions should be
positive.  To illustrate this ask someone to do exactly as you say, then tell them to close their eyes and not think about what their hands are doing.  If you ask them, they will tell you that  when you asked them
not to think of their hands, they thought of their hands.  Your visual brain can not understand the the word not.  Its like when you are riding a bike and you tell yourself not to hit a rock in the road.  You will
inevitably run right over the rock because that is the picture you have created for your brain and your brain controls your muscles.

Sport psychologist have understood this for some time and there are lots of sports examples.  Have you ever been in  the classic situation playing softball or baseball?  Its the last inning, your team is losing, the
bases are loaded, there are two outs, with you up at bat and two strikes.  If under these circumstances you say to yourself, “don’t strike out”, that is probably what will happen.  What the best batters will do is
visualize what part of the field they are going to hit the ball to.  There is no doubt that they are going to hit it, it is a matter of where they will hit it.

If you are taking an exam, or preparing to give a speech, or going for job interview, or asking someone for a date, if you say, “don’t get stressed out”, you are creating a picture of someone who is stressed out.  
If you say, “I feel calm and relaxed, I am confident and alert” then you are creating an image of someone who is relaxed and confident.

The implications of this can be profound.  If you are a parent, teacher, administrator or leader of any type, tell people what you want them to do.  Don’t tell them what you don’t want them to do.

Make affirmations short, simple and clear.  Brevity furthers.  Long complex statements are more difficult to internalize.

Use as many senses as possible in affirmations and visualizations.  Verbalize statements out loud after writing them down.  Better yet watch yourse and listen to yourself say these statements while standing in
front of a mirror.  When you visualize your performance, recreate as much of the scene as possible to create an accurate simulation.  Imagine what it sounds like, what it feels like, smells like, etc....

Make affirmations and visualizations emotional.  Imagine what it will feel like to be happy, successful, powerful, self-assured.  Visualize yourself experiencing these emotions.  At the same time work to eliminate
statements of negative emotions from your life (e.g., I’m tired, I’m sad/depressed, I’m lonely, I’m bored, I’m overwhelmed, etc...).

In summary, create and image of someone you want to become and then continue to focus on that image.  Figure out what you want to be able to say about yourself and then start saying it.