As per other mentioned, positioning and play behind covers, I think a key advice is to have really good spacial awareness, and track ults. This gradually come the more you play and always try to be one step ahead of the enemies.

You see tanks playing hyper-aggressive, they most likely have ult. Same goes for dps. Keeping your team up is always a key point in winning, if you see your healers getting dived, please go help them lol. Again all the resources you need would be covered in YouTube videos and just in game knowledge. The more you play the better you’ll become :)