Congruency basically comes into two forms that I can tell: what you say and what you do. The way this differs from the HER sh1t test, is that congruency is a sh1t test you give YOURSELF without evening know it, and you pass and fail it all on your own, without any intervention on her part. She's just a very keen observer in this situation.
During the course of conversation, things you say should match up with other things you say. No one is 100% congruent all the time (probably not even close to it), but you should not make it obvious to her or she'll start looking for more inconsistencies at this point. If she finds them regularly or find them on important stuff, she will doubt you, your value will decrease, and she'll lose interest or bolt.
My personal experience with this is that it can very quickly turn into a "snow ball" effect, where she starts too see more, look for more, see more, etc (Reticular Activating System in the brain at work here). Then she'll start making assumptions that may or may not even be accurate or have much basis in fact. Unfortunately, at this point it doesn't matter if they're right or wrong, but damage is done, since she's seen enough that she feels she can safely conclude that your inconsistent. And in congruency will also spawn the sh1t tests she gives you, once she's seen enough of them.
(examples are not always this obvious, but this will give you the idea)
Example (verbal): The HB is an animal lover, and you like animals too. Don't tell her you're an animal lover and then 2 days later, tell her how you spanked your dog for chewing up your Bruno Mali shoes.
You may in fact really love your dog and treat him great 99% of the time, and just lost your temper momentarily-but she doesn't need to know that. She'll see you as a guy who says one thing and does another.
Example (verbal vs. actions): You tell the HB you're a generous guy, and then leave a waitress a crappy tip or average when the two of you are out to eat.
The whole cheapness thing aside (which no women really likes), you once again make it look like you're "all talk, no action." Incongruent.
There are two ways I can think of to help remain congruent initially.
1) Be careful what you confide in her early on, plain and simple. You don't have to do this forever, but early on it's pretty important. If you had a really bad day at work and you're worried about losing your job, she doesn't need to know this now, no matter how tempted you might be to trust her with your feelings. It's not congruent with the "confident and secure" guy that she is looking for, that you have portrayed yourself to be.
2) No question that in the initial stages of dating, both men and women are trying to project a certain "image." It's normal. However, if you go too far in trying to project an image that's far removed from what you actually are, maintaining congruency will become an impossible task. Eventually, you won't be paying attention, and you'll say and do things that are grossly inconsistent, and she'll notice.
One Final thought: B1tch tests go both ways. You can administer them to her, and you absolutely should be watching for signs of incongruency in her as well.