Apso's make excellent watch dogs like most small breeds. Most people are scared when they hear a dog barking, plus it will alert you if someone enters your house or comes near the door. As long as you dont make it meet everyone and dont allow everyone to pet it when on walks outside the house, the dog should become fairly weary or strangers.
Food is the best motivation factor for training. Keep ur training short and reward with a tasty tit bit and you should be sucessful. Basic obedience is what you should look at, sit, come, down, no, etc.
Also get it used to you brushing and blow drying its coat along with nail trimming.