Teaching your small dog basic obedience is very important. Basic obedience allows you to take your dog with you to more places, it keeps her safe, it makes life with her at home more enjoyable and less stressful, and it enriches her life mentally, emotionally, and physically.
Which method you should choose to teach Fifi obedience will depend on several different things. It will depend on your dog, on the command that you plan to teach, and on your own personal training style preference. You may find it easiest to physically show your dog what to do by gently moving her into the position, applying a bit of pressure, or shifting her weight a bit, or you may prefer to lure her into the position and not touch her at all. If your dog loves food then 'The Treat Lure Method' will probably work best for you. If Fifi is not very motivated by food, then 'The Assistance Method' might work better. If you are trying to teach your dog to do something on cue that she already does often on her own, or something that is hard to stimulate her to do, such as sneeze, then 'The Capture Method' might be the best choice.
If your pup has ever shown any form of aggression or is afraid of being touched, then do not use 'The Assistance Method' because that method requires more physical contact than any of the other methods do.
If you are using 'The Assistance Method' then remember to be gentle. You are not pressing her onto the floor or physically forcing her into a position with your weight. For most of the commands, you are simply gently positioning her body so that she moves the rest of the way into the position on her own, or you are helping her do something, such as 'shake' or 'stand', by lifting an area of her body up a bit, or you are applying a bit of pressure so that she will move her body into the position that you are trying to teach her, on her own. You are simply showing her what to do by physically guiding her into the position or into doing the behavior that you are teaching her.
If your dog is not very food motivated or you do not wish to use food for training, then you can use something besides food, such as toys, instead. Just make sure that whatever it is, it is safe and your pup considers it very rewarding. If our dog is very food motivated and will work for her own dog food, then you can also use her own dog food, taken from her daily amount, to train her. Doing this has the added benefits of being healthier for her, keeping her from gaining too much weight, and saving other, more exciting treats for especially difficult commands.
Because your dog is small expect to get down low, on her level, while you teach her certain commands. Once she has learned a command, and can perform it when you give it to her while on her level, then in order to get her to perform the command while you standing upright also, you might have to give her that same command while you are in various crouching positions; gradually standing up more and more each time that you tell her the command, until you can give it to her while you are standing upright completely. This is because some dogs do not generalize well and a command given from a squatting position can seem different to a dog than the same command given from a standing position. If this happens to be your dog then she might need for you to help her generalize the command by giving it from different positions.
If you are using 'The Treat Luring Method' then you might need an assistant, a prop, or a treat training pouch to hold your treats for you. If you are using 'The Assistance Method' then you will need gentleness and a firm, patient attitude. If you are using 'The Capture Method' then you will need a treat training pouch or a small Ziploc bag and pocket, to keep your treats close by, and attentiveness and responsiveness.