The best way to Complain to the Kitchen
Before we get started, it should be made clear that, in most restaurants, it is impossible to complain to the kitchen. Your only option is to get a complaint to the kitchen. Kitchen staff is typically not trained to deal with customers. Therefore, managers prefer not to have them interact with customers, especially regarding a complaint. Kitchen staff is typically trained to deal with your complaint, however. If you are specific in your complaint then a competent cook or chef will be able to fix your problem.
The first thing that you want to do when you notice there is a problem with your food is to grab the attention of your server. Once you have their attention, tell him/her precisely what the problem is. Try to do this politely. Angry servers often relay misinformation to the kitchen or they get cranky with the cook who then is no way inclined to hurry for that server. It is a sad truth about the politics of restaurants. I should know; I was a cook for ten years.
You may be complaining about the kitchen, but your problem can easily be with your server and they will never admit it to you. For example, if you ordered your stead medium-rare and its medium, it could be a server mistake. This is another reason why you have to be very clear when you make your complaint. If they could mess it up a first time, they can easily mess it up a second time.
The point of complaining to the kitchen is to get new, better food, otherwise you would be simply complaining to the manager and refusing to pay, right? Therefore, be sure to contemplate your complaint and your options. If the taste was just horrible or there was obviously something funky about your dish, you may not want to order the same thing twice. Chances are the same cook will cook it and it will come out of the same batch. So, if your complaint was that the food tasted terrible or it was dubious, ask that something else be brought to you. If you are dining anywhere worth dining, this will be done without complaint.
Now, if you have spoken to your server and found them incompetent or unequal to the task of fixing your problem, ask for a manager. Of course, in a reputable restaurant, one would have been sent to you immediately following your complaint. Now, once you have the attention of the manager, follow the same steps mentioned above. Be specific about your complaint, try to be polite (no need to be ingratiating) and do not be afraid to make it clear how you would like the problem to be rectified, within reason.
This should work in getting your issue to the kitchen in a timely and consistent manner. If not, feel free to demand your bill with none of the complained about food charged to it and none of the food you have not received yet. Chances are you will not be expected to pay for anything unless you are part of a group where a portion of you has been served satisfactorily. No restaurant should have its doors open if complaints about food are not heard and dealt with in a friendly and professional manner.