1. Stop using the food as a bribe. When a dog is first learning something, luring/bribing him with food makes things easy for dog and human. Toss a piece of meat into the back of the crate and, voila, the dog goes in the crate. Hold the food in front of his nose while slowly lowering to the floor and, whammo, the dog lies down. This is a great way to train but it is very important to FADE THE LURE as quickly as possible. One must quickly get to the point where the food is out of sight but readily available as a REWARD. After several times of luring the dog into a down, use your empty (but still food-stinky) hand to motion your dog to lie down. Once he is down, quickly - and I mean QUICKLY- give him the food that you have been hiding in your other hand.
2. Keep food hidden and in various locations. One can use attractive glass or ceramic containers with lids to place around the house to keep rewards available but out of sight. Instead of wearing a treat pouch at my waist, I sometimes clip a Ziplock snack bag to my shirt collar so the dog has more difficulty detecting food on my body.
3. Delay the reward. Once the dog is proficient at the sit, start delaying the reward by very small increments. Count one second then give reward. Do this 6-8 more times then count two seconds and give reward. Work up to 10 to 20 seconds before giving a reward. And, guess what? You just built in an automatic STAY while doing this!
4. Have the dog do another behavior. After the dog sits for a few seconds, release him and run to the door and toss a treat outside. Or, after the dog sits, release him and run backwards calling him to you and give food. Or, after the dog sits, send him to his kennel, have him lie down, then give a piece of food. Start adding in more behaviors in the chain of events before he gets the food.
5. Start fading the the food rewards by giving food on a random schedule. Skip the reward every third or fourth time you ask for a sit. Switch it up for awhile then start reducing the frequency of food rewards.
6. Use other rewards in place of food. Request the sit or down before you let the dog greet you when you enter house, greet other people, go outside, get in the car, throw the ball, etc.
The BIGGEST and most detrimental MISTAKE people make when using food rewards during training is they bring out the hidden food and show it to the dog if he doesn't perform the behavior when asked. This is a big, and I mean BIG mistake! The only thing your dog learns is to hold out until the food appears.