how to teach down

There are many way to teach your puppy to down.

As mentioned, there is clicker training (you can use an actual clicker, or just use a "marker word" such as "Yes" "bingo" etc). In clicker training, there are basically 3 ways you can use the clicker to get the desired behavior:
1. Lure. Use a treat in your dominant hand and hold the clicker in the other. Have puppy start in a sit and place the treat/hand directly in front of her/his nose. Slowly take the treat down toward the ground. Stay close to puppy's body. If you move it too far away, puppy will get up and walk towards the treat. If you keep it too close to the body, puppy will jump up from sit and stand and back up. Go directly down toward the ground. The instant puppy's elbows are on the floor, click or use your marker word, and treat. (read earlier provided links for info on "priming" the clicker or marker word) I do not use a command (The word "Down" or "Platz") at this stage in the training. Wait until you can reliably bet that you can get the behavior before you give a command. If you want your puppy to learn to respond to the command on the first time he hears it "Down", then repeating the command several times is not a good idea. Puppy will think it was that 3rd or 5th utterance of the word that was rewarded, not the first. When I do start adding the command, I only give it once.

2. Shaping - Have the clicker or marker word "primed" Closely watch your puppy. You are going to "mark" and reward every little picture frame (think movie frame) in the process of him/her going down. At first it may be looking toward the ground that you mark. Then a lowering of his/her head. Then a foot moving. Then that foot moving out forward away from the body. Then a hunching downwards.... Keep reinforcing behaviors that eventually will be the end result of a down. Again, no verbal command to get there. Let the puppy figure it out. This one takes patience and good timing along with knowing what you are looking for and when to keep "upping the ante" toard the end result of the goal behavior.

3. Capture - Wait around with treats in your pocket. Anytime you catch your puppy in a down "mark" it with a click or the marker word. this one takes longer sometimes just because you have to wait for the opportunity to catch him already doing the behavior.

Of all three, the first, Luring, is generally the easiest way to start training the down for many people. One of the biggest things, IMO is not to start giving a command until the puppy has an idea of what behavior earns a reward. No point in repeating the command and confsing puppy as to which one was rewardable. Wait until you can safely bet you can get the behavior (either through luring or that puppy is consistantly offering it on his own), before putting a command on the behavior.

Good luck and congrats on your new puppy!