Teleporting back to the ship

The combat effectiveness of your crew varies, and additionally they level up as they fight.

For instance, Engi and Zoltan crew members have lower health than Humans, Slugs, Mantis, or Rock crew members. Mantis crew also have a bonus to combat damage. Engi and Zoltan especially are worthless in a fight - be ready to move them quickly, and plan on any combat taking a while if you can't get the enemies into the medbay quickly.

I tend to assign at least one, but ideally two of my crew members to "security detail" - they're the ones that get pulled into rooms to fight if there are enemy boarders. They're also typically my away team if I have a teleporter. I will tend to pick Mantis first for this, then Rock, and finally Human. If I've got to double up and have my subsystem crew work security detail, I tend to leave the weapon officer and pilot alone - other crewmates will pull security detail before I'll move them.

Some other tips:

• As has been noted, the best place to fight is in your medbay, as you'll constantly regenerate health so long as the medbay is undamaged and powered up.
• I will sometimes open doors to route enemies into 2-square rooms, or let them have a particular subsystem (ie, sensors or door control) if they're likely to move into a more advantageous room after they've damaged it.
• Remember that you can pause (with space) and issue orders - if you need to shuffle crew around, and you've got a lot going on between ship combat and dealing with boarders, this can save your crew, especially if you're like me and you tend to click doors rather than crew in a panic.
• In combat, you'll still take damage as long as you're in the room with the enemy, so make sure you leave enough health on your crew to make it out of the room before they die.
• If you've decompressed part of the ship, remember that you'll take damage passing through it, so keep that in mind as well if the decompressed portions of the ship are between your crew and the medbay.
• Upgrade doors will help a lot, giving you more time to "vent" them to death or time for you to finish the fight with the ship before taking care of the boarders. Just remember robots don't need oxygen and if your door controls get destroyed you can't close doors, which means you could lose oxygen.

The Anti-Ship Drone is armed with a laser, which does damage to a single room targeted randomly by the drone. It also takes the shields down one level if it hits a shield..

The Anti-Ship Beam Drone is armed with a beam weapon, which does damage to multiple rooms along the path of the beam, but which does not affect shields at all. Instead, shields affect the beam, in that each level of shield reduces the damage of the beam. Since the Anti-Ship Beam Drone only does 1 damage per room, even a single active shield can render the Anti-Ship Beam Drone completely useless.