To dream of a line symbolizes duality and flexibility. It may refer to changes or status quo. A line is also indicative of your personal limits and boundaries. Hence, to dream that you are crossing a line suggests that you are testing your limits, stretching yourself outside your comfort zone, or simply doing things that you would not normally do.
To see a line of people or objects denotes that you need to be keen about your surroundings and observant of people.
To dream that you are standing in line signifies your need to be more patient and tolerant. You should learn to wait on something without losing your composure.