play other champions to learn their "potential zone of threat" aka how close that champion has to be to kill. Then stay out of that zone.
Pay attention to the mini map, if someone is missing, think about where they might be and whether they may be threatening you.
You sound like you are good at fighting. Before you go in, consider: where do you think the jungler is? don't know? assume he's near by to back up the enemy.
If you say, spot the jungler on the minimap on the other side of the map, and you can see all 5 enemy champions, and know that it's a fair fight then feel free to do your thing and fight.
Try to judge fights and whether or not you should go in. Don't be too cautious with this, as hanging back too much will result in the deaths of your allies which is also bad. Sometimes you gotta trust your friends and fight with them even if you aren't sure if you can make it.