Visualise any simple fruit. One you can recall the texture of, as well as the scent, taste, shape, and sound of (when bitten into). Examine it fully for as long as you need. This may take days so pick a favorite fruit.
Once you feel you know that apple inside and out, set it aside and try to create a mental image of it (from top to bottom and side to side). Then try to grab it and it and feel its texture (if your working with a fruit that peels, notice the inside texture as well). When you are able to do this, take a bite out of it. Notice the taste. Begin to feel your mouth water as if it were really there. Notice the sound it makes as your teeth bite into it as well. Last, take a piece, or the whole thing and bring it up to the nose.
This may take a bit of time and practice but well worth it. The last step I would suggest as well is to open your eyes and see if the fruit you are eating is there in your hand.