How to choose betwen fight and farm as a mid player?

Helló

First of all sorry for my bad eng knowlage

So, i prefer to main pos2 aka mid. The mid job is one of the (if not the most) importent in the game. At the lane phase, you help the others, you try to crush the enemy offlaner and you try to set Back the enemy safflaner, in the middle part of the game, you make the space for you pos1 and you try to crush the enemy space and farm. You choose how agressive or defensive your team.

For this, you need tools. Like XP and gold for items. For this, you need to farm. How do you choose when you farm and when you go and gang or try to dominate the enemy side of the map? If you try to gang too much, and fail a few Times, you find yourself under leveled and under farmed. If you dont help your team enught (pos 3-5) they suck and Just die for the enemy team advantage. If you force your team to play too defensive you give too much free space for the enemy in their side and the chance to dominate your side. If you play too agressive, you risk a lot

So. When you go and fight and when you farm?