Part 1: After clearing your mind through meditation, visualize a familiar object such as a box or something you possess. Let it be an object you would see on a regular basis. Hold that object in mind for as long as possible. Visualize its color, tecture, shape, etc. When you can hold that object for more than 5 seconds, move on to part 2.
Part 2: After clearing your mind through meditation, visualize an object you have never seen, nor would ever see on this plane of conciousness, such as a fruit from Mars. Use your imagination. It can be as simple as a furry, purple, square shaped fruit, or more complex such as the same but with orange spots and green hairs. After you can hold this object in your mind for 10 seconds or more, move on to part 3.
Visualization and meditation is important for spellcraft. Once you have mastered clearing your mind and Part 2 of the visualization, you'll be able to work spells with ease.