Use the following tips to more effectively engage enemies on defense and give your team an advantage:

Do not attack the enemy right outside their spawn. If you die, they will be back in the fight much quicker than you due to you having to spawn further away. This is especially important at the beginning of a match.
Engage the enemy at a choke point where you have the advantage. It is best to also have the height advantage while defending a point. For example, while on defense on the Route 66 map, do not defend the payload near the enemy spawn. Setup and initially defend around the corner on top of and around Big Earl's Gas. The enemy will then be further from their spawn and you will be closer to your spawn and have a better overall advantage compared to defending near their spawn.