Unlike Beckham, known for his long, elegant, arcing crosses with a metric-ton of English on them, Ronaldo's crosses are more like little behind-the-back passes in basketball. He takes the ball deep into enemy territory, then pops it into the air back across the field of play toward a team made for a header or a shot. Though he often plays on the left side of the field, Ronaldo also switches, depending on the play as it progresses, and will go to the center to take crosses as well. To pop a Ronaldo-style cross, make contact with your foot straight, and your plant foot well-behind the ball. Make your follow-through very short to pop the ball up as much as possible, giving your teammate an opportunity to get a head on it. One of the freakiest things about Ronaldo is that he seems to be just as good from both feet. His left-footed crosses and shots are just as wobbly and accurate as his right-footed crosses. Work on your non-dominant footwork by doing dribbling drills with both feet, and taking as many wrong-footed shots on goal as possible. Practice your fundamentals until you can get the right kind of power from both feet, even if it feels backwards. Ronaldo's footwork makes him able to get the crosses off in time, making his play unpredictable and thrilling to watch. If you want to be able to take the ball that deep into territory, you're going to have to be able to evade defensive players and juke them out of their shorts. Practice step-overs to imitate Ronaldo's great dribble. Also, try to practice his distinctive behind-the-leg direction switching pass that he does to himself.

Summary:
Take the ball into the box. Pop the ball up to a teammate. Develop your cross from both feet. Control your dribble with step-overs.