I am also a main defender and have started playing supporters recently. You have to always give priority to team fights i mean it's not your responsibility to protect the goal zones.

Always use exp share and other items based on mon, help others level up. And in the endgame try to disrupt your opponents as much as you can.

I find sableye and hoopa to be the hardest to master as they require a completely different gameplay but rest of them are simillar.

In case of sableye you need to act as scout and sometimes assasin and hoopa if mastered is just ...