what is the best way to grind?

This is one of the most obvious ways in which you can quickly get a large amount of AR EXP. The main, side and daily missions offer a large amount of AR EXP, which may come in handy if you want to quickly reach a particular level. If you need a quick boost of AR EXP, try to complete as many quests as possible. While doing a particular quest, you should know how many AR points you receive for completing it.