Nothing In Life Is Free
The cornerstone to teaching your new foster pup patience, politeness, and deference to you is... Sit.
First, of course, you need to teach her to Sit. Luckily, this is an easy one; some foster dogs will arrive already knowing it, and the rest usually pick it up within a day. You may have to lure it or use a hand signal rather than a verbal cue, but even a half-trained Sit is enough to get started -- and, with lots of daily practice, it shouldn't take long to teach into its final form.
Once she has that down, whenever your foster dog wants anything, ask her to Sit first. Before dinner, before she gets to play with any of her toys, any time she wants attention from you, and for anything else that comes to mind (except possibly potty walks, if you're still in the process of housetraining). Nothing in your foster pup's life is free. She has to work for everything, and that work is: Sit.
Your dog may initially need help understanding the game, and might not be able to focus if she really wants whatever reward is in store. Be patient, especially in the beginning, and scale the criteria down to your dog's current ability level. If she can only hold a Sit for a microsecond, but you know that she's really working hard to get that microsecond, reward it. That's good enough for now!
If she can't even do that, try putting away the food bowl or setting down the leash and walking away from the door. Wait until the dog seems calmer and then ask again, without the overstimulating object in view. Then bring it out when you've gotten an acceptable Sit, so that the appearance of the object becomes part of the reward instead of a distraction.
As your foster pup gets used to the basic idea, you can raise the criteria. Ask him to move away from the object he wants (after you make it inaccessible by raising it out of reach or putting it inside a closed crate) and toward you, prompt for a Sit, and only then hand over the object. Be patient; it may take a minute for the idea to click, but it's well worthwhile. This exercise teaches that impatience gets nothing, that all good things come from you, and that the surest way to get those good things is to do whatever you-the-trainer request. Thus, every time you do it, you're building your foster pup's impulse control and establishing your relevance as the giver of good things.
While practicing the NILF protocol, you should also continue training the rest of the Obedience 101 curriculum and (if you choose) a couple of tricks. Prompt for those tricks once in a while, instead of asking for a Sit every time. It never hurts to get a little extra practice in, and it keeps your dog on her toes.
The cornerstone, however, should remain Sit. After a few days or weeks of this, depending on your foster dog's natural tendencies, she should offer Sit as a default behavior whenever she doesn't know what else to do. At that point you can start scaling back the NILF protocol, although it doesn't hurt to keep it going and I would recommend at least continuing to request tricks and obedience behaviors before meals and other high-value events. You can also start building longer duration and better concentration into the Sits by asking your foster dog to hold it a few more seconds, or ignore a couple of mild distractions, before earning the ultimate reward. Everything in the training program should reinforce and build on everything else; NILF is really just another way to practice and reward good behavior.
Here are two quick clips of my foster mutt Crookytail practicing NILF a little over a week after his arrival: Level 1 (Sit gets the marrow bone) and Level 2 (in order to get his dinner, which is locked inside his crate, Crookytail has to move away from the crate and toward me, Sit, and only then get his reward).
The concept is very simple, and practicing it is easy, but "Nothing in Life is Free" is a powerful tool. Make it a rule from Day One, and you'll have a vastly better-behaved dog.
In the months after I originally wrote this post, Kathy Sdao released "Plenty In Life Is Free", a booklet arguing against the more extreme versions of NILF. She makes some very good points (some of which are discussed in Patricia McConnell's blog post on it), and in light of that, I want to reiterate that the purpose of this program is to quickly establish a positive relationship between yourself and your new foster dog, and not to punish the dog for failing to comply. You should never deprive the foster dog of basic life necessities -- water, opportunities to potty outside, and basic sustenance (if your foster dog really cannot Sit for a meal even after several tries, go ahead and feed the meal anyway; you can try it again next time).
I know this should be obvious, but evidently there are some trainers who take it to extremes, and so I want to make it very clear that depriving your dog of necessities for "failing" at NILF is neither recommended nor approved.
And you don't need to keep NILF going forever. It can be relaxed once the dog clearly understands the equation of patience + good behavior = prizes!! I don't recommend discarding it altogether, because it is a very useful tool, but it should never become a straitjacket for you or your foster pup. Think of NILF as the behavioral equivalent of a crate: it is an extremely useful piece of equipment that, pushed too far, can become counterproductive or even abusive. But use it mindfully, and make it fun for your dog, and it will serve you well.