Whenever I'm on defense I'm always in the objective room waiting for the enemy team to attack I'm not moving out peeling corners where the enemies are just to get killed. The whole point of defending is waiting and letting the enemies come to you. Unless you're a roamer but when you pick an objective operators let the enemies come to you.
Seriously is nobody using thatcher and thermite anymore?
One of the biggest mistakes I've noticed new players tend do is that even though a teammate has two reinforcements on a two reinforcement wall, they feel as though they should help finish it. You can save yourself and your teammate the hassle of running around looking for an open wall, by just choosing a different wall to fix up. It should be common courtesy, but I've found that many people don't even realize what they're doing.
I've been trying it with a friend over the last few games, and it works like a charm. No one expects to explode while jumping over a deployable shield. Worked 5 out of 8 times we tried it, not including matches where they didn't even go that way.