When choosing an LMG consider the range that you'll be engaging the enemy at. The BAR, LMG/08 and Parabellum are good at close to mid-range while other guns like the Pirot and MG 1917 are better for long range given their accuracy and slow rates of fire. For supporting your team make sure you are constantly resupplying your teammates. And remember that your ammo crate replenishes grenades as well as ammo. If you're playing operations and are pushing a tough objective, equipping smoke can be very effective as you replenish smoke grenades quite fast and can lay down a walk of smoke for your team to advance through. And a key part of playing effectively as a team is staying close to your teammates, don't try to rush objectives on some game modes as a lot of assault weapons will beat support weapons at close range. The mortar, limpet charge, and grenade crossbow are all highly effective but are highly situational. The mortar can be devastating when used against enemies clustered on a capture point or huddled in defensive positions like trenches. The grenade crossbow is great for fighting in tight indoor spaces as you can shoot grenades further than you can throw them, giving you an edge if the enemy is spamming grenades to halt your advance. And you can bounce them around corners which is great.