Don't Leave Games
If you can help it, stay in your Battlefield 1 matches until the very end.
There might be times where you're frustrated. Maybe you're getting wiped out by a better team. Maybe your aim is off. While you might be tempted to leave, there are some very good reasons to stay.
When the match ends you'll receive some bonus experience. You'll get an end of match bonus and you might also get some XP multipliers. Depending on how you did in the match, these experience bonuses could be big so you'll want to stick it out.
You also might get a Battlepack to open. These contain bonuses and gear. Battlepacks only drop at the end of the match.