The down on command is extremely important and can save your dog's life if properly trained.
If for some reason, you have your dog off lead in a park and he sees a cat across the road, you will be very glad you trained him the down on command.
Of cause it will take many repetitions before he will be so conditioned to stop in his tracks and go into a down position, when he actually wants to chase that kitty.
For your dog the down is a very passive thing, almost a negative thing.
Normally they want action.
So you should be careful when you work on the down so it does not become boring for the dog.
The rewards that you use, your praise and treats, must be plentiful.
In competition Fido will always be at your left in the heel position and he should be able to do a down from the sit or stand position and also on the move.
To start the training of the down, it does not really matter where Fido is in relation to yourself, because at this point you are only focussing on the down itself.
This is how you will teach your puppy to down: Let him sit on your left or in front of you.
Take a treat in your one hand and clicker in the other.
With the treat lure him into the down position.
You do that by holding your hand with the treat in front of his nose and moving your hand down to the floor.
Normally it only takes a second.
The moment he is in the down position, click and give the treat.
Repeat that several times.
At this stage you don't say a word, you don't give the command "down".
After about 20 repetitions you can start giving the command as you lure him into position.
Your hand movement should be very fast to encourage your dog to do fast downs.
Now after another 20 or more repetitions you can test your dog, by doing the hand movement but without a treat.
Just give the command as you move your hand.
The moment Fido goes into the down, click and give a bonus treat.
Make a big fuss and repeat again a few more times.
Do not try to progress too fast, but rather lay a solid foundation.
If at any stage you test Fido and he does not respond quickly, go back a few steps.
Up to now, obviously, you have been bending down to lure your dog into the down position.
Your back is aching and you are running out of pain killers.
You do not want to bend over every time you give the down command.
On the other hand Fido is not going to respond on the first down command if you all of a sudden don't bend down.
So you need, or rather Fido needs, a transition period where you still bend down, but not as far.
Here again, make a huge fuss and give lots of yummy treats if he responds correctly.
Always set your dog up for success and remember to keep training sessions short.
Do not try to do the above in one session.
It should be done over many sessions so the down command will almost be engrafted into your dog's mind.
Only then will he immediately respond when you give the command even when he is actually chasing a cat.