I usually start them off by taking a thin wedge of apple and when they are chewing an insect put the end of it between the chameleon's teeth....or if it's annoyed slip the end of it between the chameleon's teeth. This let's them taste it. I then impaled wedges of apple on a branch in the cage so it can eat it when it wants to.
Don't give them too much fruit though.
You can offer them pear,apple, berries, melon, etc.