1. Positioning! If there is an enemy in front of you and not a teammate in between, you're probably not where you need to be
2. Don't be afraid to scope in, it makes her rifle hit scan which is great for countering Pharah, Widow, etc., But be aware that enemies can see your bullet trail this way so don't do it from the same place for too long
3. Communicate when you're ready to ult, always try to combo if you have the time to set it up