The Waltz is an old favorite for Wedding couples and the beauty of a slow Waltz is the 3/4 timing, i.e. all steps (at least for beginners) are single beat steps. No need to memorize: "Quick-Quick-Slow" or "Slow-Slow-Quick-Quick" as one must for the Foxtrot or any of the dances that have four beats to a measure. The first caveat: "Don't step on the bride's dress!"
Of course the Box Step is preferred by beginners since there's no need to travel around the floor and it lends itself to a simple underarm turn by the lady.
In the Box: the man leads forward with the left step (lady back on right). (from here I just discuss man's step since the lady's is simply the mirror image of the man's): One the man moves forward on the Left and begins to plant his foot, he lifts the right foot and with a small curving movement (no right angles and no hypoteneus)moves his right foot to the side of his left foot (approx. 12" apart). He then brings his left foot next to the right and plants it. One his weight is on the left, he moves his right foot backward and plants it, on the next beat, the left foot takes the curving movement backward to be planted approx. 12" to the side of the right foot. Once the left is on the floor, the right foot is then brought to close next to the left. You've just completed one "box." The timing is all single beat. Since the music will be slow, you're not really stretched to hurry. Now, to look like a dancer, you must use a little "rise and fall" with the Waltz. There is a rising movment (up on the ball of your foot)on beat two. It is a smooth movement, not jerky, which means you really start rising at the end of beat one and drop the rise at the beginning of beat three. Now, if you dance flat footed, the only way you'll get a rise and fall is if you go up on your tippy toes on beat two. Not good! So that means that the whole dance must be done with some knee bend throughout beat one and three, and straightening the knee on beat two to make the "rise." One final addition to make your box step look good: The Waltz is a turning dance so even your basic box step must have some turn to it where partners revolve around each other at whatever rate is comfortable for them. Of course the more revolution around your partner the smarter it looks. The turn takes some practice in order for it to come naturally and flow from the shoulders down. Best to start by practicing simply turning your toe out on the forward step and the heel out on the rearward step. Your shoulders and, hopefully, your partner will follow your feet into a turn.
Finally, stance (frame or posture). In the Waltz you both want to be upright with a little arch to the back and butts tucked in. Man's left arm is extended in a (natural)slightly bent at the elbow position. Left hand holding the lady's right hand, palm to palm. Her right hand should be at her eye level. Both man and lady should have a degree of muscular tension in the extended arms. (Makes it easier for the man to lead and the lady to follow.) Man's right hand is on lady's left "wing" and his right elbow is supporting the lady's left elbow. Lady's left hand is on man's shoulder and, for novices, keep the thumb in front of the man's shoulder to provide a little "push" tension, keeping the man at his distance and not letting him override the lady. So, you now have four points of contact: (1) Man's left hand to lady's right hand; (2) Man's right hand on lady's back; (3) Man's right elbow under lady's left elbow and (4) Lady's left hand pressing gently on man's right shoulder. Now find some nice slow (98 beats per minute) waltz music and GO TO IT. Don't wait until the wedding reception to practice!