"Lex orandi, lex credendi" literally means "the law of praying [is] the law of believing." Another way that this phrase is rendered is: "How we pray is how we believe." This statement indicates the power of gesture, ritual, and symbol. These are a reflection of belief, but they also shape belief, for good or for ill.
How we enter a church is a good example of this principle. If we come in and simply walk into a pew, our gesture indicates that we do not believe (either explicitly or implicitly) that Jesus is truly present in the Eucharist reserved in the tabernacle. But if we genuflect before entering the pew, and specifically genuflect toward the tabernacle (wherever that may be), then we are reminding ourselves, and acting as a witness to others, that we believe Jesus is physically there. But if we genuflect toward the front (in effect, toward the altar) when the tabernacle is not situated there, then our way of praying is a habit rather than an assent, an affirmation.
After mass, my family and I go up to the tabernacle to pray. (We never used to do this, but have been doing so for a while now.) Although we have received Jesus, although we ourselves are for the moment "tabernacles" (since we actually, really, physically carry Jesus within us), going up to the tabernacle reinforces this. Think about Jesus, at the Last Supper, where he is both physically present in his human nature and then also Eucharistically present in the bread-turned body and the wine-turned blood. That act is not redundant, it's not superfluous. Rather, it's super-abundant. But if we receive communion and immediately leave, what are we saying about what we have just received? Are we treating communion as a kind of "fast food"? Are we saying, "this is merely bread, this is merely wine"?
When my family and I pass a Catholic church while driving, we acknowledge Jesus' presence there. My wife and I make the sign of the Cross, while our children, who are 5 and 4, say "Hi, Jesus." I try to do this even when I am in a car with other people (although I am still somewhat self-conscious about it). This can be a very important witness to others, even other drivers simply passing by when you are doing this. We want our children to internalize and reinforce belief in the Real Presence. If we can instill reverence for the presence of Jesus outside of the church building, perhaps that will increase our reverence even further when we are inside the church and in close proximity to Jesus himself.
I don't mean to imply that I and my family do this perfectly and that others are don't. This is a reminder to myself that I can and need to do better, to do more. We cannot show Christ too much reverence, reverence which is due to him because of his nature (for he is God) and because of his sacrifice (for he is our redeemer).