When you clean your windshield with a squeegee you automatically put pressure to get a good cleaning. The same should happen with your wiper blade. If there is no pressure, streaks will form and you will have to wipe again.
Streaks are also caused by dirt, ice or snow accumulation on the wiper blade. This dirt will prevent a tight seal and cause streaking. Although cleaning the wiper blade properly will help, road conditions cannot always permit to drive with a totally clean blade at all the times.
Although less frequent, a slight concave malformation of the windshield during its manufacturing process can create a gap between the wiper and the glass that will generate blurry spots.
One sure way to prevent streaking is byadding pressure to the wiper blade to get a snug fit against the glass. Sure Wipe add-on wiper arm spring were created to do just that. They increase pressure on your wiper by 30 to 50% with no harm to the wiper motor as tested. The blade having more surface of contact with the windshield will be more efficient. It will flip more energetically on the return stroke and leave all debris like snow, ice, or dirt behind at the end of the stroke instead or dragging them back and forth.