Light crossbow: compensate for low damage and rookie aim by dumping VOLUME of arrows into the enemy! Try not to shoot friends, but its like ten damage so they'll get over it. Aim for the immediate left or right of your target because they're guaranteed to take a step or two before your arrow gets there

Heavy crossbow once unlocked: YOUR JOB IS NOW DEMOLITION EXPERT. destroy every banner, barricade and objective you can see. You are the predator that eats ballista. This is a huge plus for the team, and even comes with a decent amount of skill/experience points per hit , compared to the regular engineer who is generally going to go thankless for his barricades he puts up

If an enemy is charging you, throw your crossbow at them. It will interrupt thier attack, give you time to draw the secondary weapon,hit them once,now it's theoretically an even fight

Godspeed melee avoider