I hesitate to add after gallen's positive instruction, but...
Two phrases I've used Before doing meditation are:
"I give myself permission to use this time only for my meditation. I choose to use this time for my meditation".
"I choose to experience the meditation fully and completely, and leave all analysis and reflection of the experience until after I have completed my meditation".
I just use these statements as intentions I'm communicating to myself. They are not rules that have to be followed.
Remember to honestly smile, and to smile at yourself should you notice your practice is not what "you think" it should be. Because is it perfect the way it is, right now. It may be different later, and it will be perfect then too. It is always exactly what you need for you purpose. Express gratitude at the conclusion of your meditation for your experience and your guidance.
You are perfection.
Iam2 
