Opening doors aggressively but safely is almost a mini-game. Always plan for the new monsters taking immediate actions. You want to be as healed up as possible and have as many ability and item card options available as possible before cracking open another room. Resting just before opening doors if you're almost due is often prudent. You may want to take a turn to cast some persistent buffs while you're not under enemy pressure. You'll want all your characters close to the door when it's opened so they can contribute quickly. But you don't want to waste too much time to get ready before opening every door. Try to have your door-opener reserve at least one extra hex of movement available to your after the door opens to either retreat or advance to a better tile. If you're a melee character, try to have either a ranged attack prepared or additional movement ready (boots) so you can immediately make some sort of impact. Know the rules for LOS between hexes, it actually takes quite a sharp angle for LOS to be blocked around doorways and more often than not both sides are easily targetable.