Pubg's Duo mode is of two players teaming up together and play a war. Duo mode is availabe in both Classic and Arcade. The classic mode is of 100 online players were all battle together as a team or solo. Here are sone tricks for you when you play duo in classic mode.
1) Teamup Together
Always land together in the place were there are houses and never get spilted so it will be easy for enemies to kill you easily. You cannot ask for help when you and your teammate are too far. So in the parachute landing follow your teammate and land in the same place.
2) Secret Places
Find secret places after collecting all loot and guns. All the players will try to gather center point of the map so its better that you and your teammate rush in before the other players get in there. Search for rooftops or any place were you can hide and spy on enemies.