Well, first thing you do in any sort of scenario like that is probably pull the fire alarm to alert the rest of the crew to the danger. The fire is burning in a high oxygen environment though, which means it's burning hot, and that we don't have much time. If there's fire extinguishers on hand then that's an obvious choice, but fire on starships needs to be treated especially aggressively so I would consider venting the room into space. I'd prefer to have respirator mask for this part of it (though the vaccuum of space would still fuck me up) or if the spacesuits are present rather than just their o2 tanks then I'd put one of them on before the venting took place, but human beings can survive the vaccuum of space for a little while and in any case the fire will kill me anyway.

In short, pull the alarm and activate any built in fire suppression, equip vaccuum protection, vent the room. Failing all else, I can use the O2 tanks I've been filling as a personal supply of oxygen when the room is vented, though at that point it'll be the negative pressure that is the true danger.

Exhale during decompression, lads, or your lungs will burst and you'll die of massive pulmonary emboli.