Training Puppies
My chi pups are accustomed to being petted and carried, and they are
comfortable with adults and older children.  When they are old enough,
they go outdoors twice a day for playtime.  When you take a pup home,
this is a good routine to follow to encourage cleanliness and scheduled
potty breaks.  Expect housetraining to be a gradual process.  If you have
carpets, limit your pup's territory to only hard-floor areas until
housetraining habits are reliable.

Safety precautions
Since chihuahuas are very small, they do not need to have the run of
the house.  Access to all rooms may even be dangerous due to hazards
of electrical cords, food, furniture, children's toys, etc.  Chi owners must
be especially vigilant when taking them outdoors, as tiny dogs are
vulnerable to being attacked by dogs or cats, stolen by humans, eaten
by hawks, or lost through minuscule gaps in fences.  I have heard many
tragic stories from people whose tiny dogs were thus killed or lost.  It is
wise to supervise your chihuahua whenever he goes outdoors.  On
outings or walks, keep him on a leash or inside a purse.  Anytime he is
on the ground, be ready to pick him up immediately if another animal
approaches.  Keep your chi near you and never use retractable leashes.  
Anything can happen when your pet is outdoors, even in your own yard.

Agility & performance
I routinely train my dogs in agility for fun and exercise.  They enjoy the
activity, and it helps them learn trust, obedience, and coordination.  In
agility, the owner or handler leads a dog over and through various
obstacles such as an elevated dog walk, teeter-totter, weave poles, and
jumps.  To earn points toward titles in agility competition, the dog must
properly complete a set course in a limited time frame.  If you are
interested in training your pup in agility, obedience, or rally, I can
provide information on how to get started.  Agility classes and
competitive agility events take place all over the U.S.A.  American
agility clubs include AKC, NADAC, and USDAA.

If you are looking for lightweight, portableagility equipment that is
scaled to a smaller size for little dogs Holbrook Dog Training Custom
makes excellent mini agility equipment sets.