First... a hungry puppy. Skip a meal and use the training treats as food. I prefer Bil-jac or Natural Balance roll, roasted chicken.... something that is "real" food and not junk. Very small, one swallow, pieces.
I start with it in my hand, then in a pouch, then quickly to a bowl placed strategically in the room. If you "lure" too long, you will never recover. Speaking from experience.
Second.... where will you train? Always start an exercise in a low stimulus environment. I prefer the den, then move to my yard, then the park, then Petsmart/Petco. You get the idea; progressively more difficult. This may take 6 weeks.
(Remember, if your puppy holds eye contact for 30 seconds in the den, go back to 2 seconds when you change locations.)
Time of session.... I use the commercial break during a show. No longer than that for each session.
I use "ready" in a happy voice to indicate start of training, and "That'll do" in a low tone to indicate the end.
Be a vending machine. At first the puppy should not really be nudging hands. If puppy is nudging, you waited too long. Don't ask for perfection at first. A glance in the facial area works.
(This is where the clicker comes in super handy if you decide to use one).
Then glance for one second, then two, etc.
Be The Chihuahua..... In other-words, be energetic, move around, and talk to your dog in a voice that gets his attention. If you need a high pitched squeak.... do it