Imagine picking up the instrument. Feel the weight of it and sense the wind blowing through the horn as you play great notes. If you have an upcoming performance, make it even more realistic by picturing yourself in the hall, the sounds of the audience, and the feel of your concert clothes. Now try playing the piece on your instrument. Another goal-setting technique is to focus on what you want to communicate to the audience.
Music is communication, and requires a composer, an interpreter, and a listener.
You are telling a story through your horn. You are the medium with which composers create their art, channelling their feelings and emotions through you to the audience. Of course, don't be afraid to put your own stamp on it, because your individual statement is what makes it interesting. Keeping a goal journal is a good way to motivate yourself to practice. I often have difficulty practicing for an upcoming symphony concert when continually rehearsing and performing various gigs.