Mow your grass with long, even passes back and forth. For example, if you mow one pass east to west, when you reach the end of the lawn, turn the mower around and mow a stripe west to east.
Walk the lawn roller over the grass in the direction it was mowed. If you mowed a stripe east to west, roll that same stripe east to west as well. This will push the blades of grass in that direction and give the impression of a stripe in the lawn.
Mow around the perimeter of the lawn, then roll over this perimeter pass to clean up the marks left. This will give your lawn a clean border.