[Lizzie07]

First teach him to "look." In a quiet place, with no distractions, have him sit in front of you. You can sit on the floor with him in front of you, or on the sofa, even. With one of his favorite cookies, let him follow the path of the cookie to your eye level. When the cookie is at eye level, say "look" and when he meets your eye, speed that cookie to his mouth saying "good boy." When you think he is beginning to understand, then you can intermittently just praise him, slowly. Also, once he has it with you sitting down, practice with you standing.
Don't use the "look" command in real life until he really has it down. Once you do take it out, be proactive and try to see the dog or distraction before he does. As soon as you do, tell him to "look" and be sure to treat. Treat it (pun) like he's learning it all over again, using cookies, when you introduce the distractions, before just relying on praise. Always praise when you treat.
When I first start training something new, I use extra special treats. Also, the harder it is, the more special the treat.
A tip: everytime I give a cookie, I throw in a "here," also. I've saved more than one agility run from an off course by saying that. I've also used the "look" command to keep a dog on course.
Good luck.