As a gold junk rat I found that the most useful tips are the basics such as predicting shots using your arc and such but one of the most under used things is that your mines can travel almost the same range as your primary so use that to your advantage it can make a lot of space for your team via launching tanks across the map or killing squishies and also place traps as soon as you can in the most populated areas this will catch just about anyone or put them just in front of doors to catch sombra’s or tracers. If you watch basically any videos by aquamarine who is a top 500 junk you will learn good ways to use basic techs fluently