First, look for wires. If the tree or any limb is touching a power line, a service drop to the house, or a downed cable of any kind, stay away from it and call BGE or Pepco before you call us. Tree crews cannot legally work on a tree in contact with energized lines until the utility has made it safe, and neither should you.
Second, check the structure. If the tree is on the roof, look for sagging, cracked drywall, or doors that suddenly stick, and if you see any of those, get out of that part of the house. A tree that has partially fallen and hung up in another tree or on the roof is under tension and can shift without warning. Don't cut it, don't climb on it, and keep kids and pets away.
Third, take photos from a safe distance. Your insurance adjuster will want them, and a good tree company can plan the crew and equipment from your pictures before anyone drives out. Note the time and, if you can tell, which direction the tree came from.
Then call. In Maryland, anyone you hire for tree work must hold a state Tree Expert license, so ask for the number. Storm removals are rigging jobs: the tree has to be lifted off the house in sections, often with a crane, without adding to the damage. That's not a chainsaw-and-a-pickup job, and the cheap quote after a storm is usually from someone who doesn't know that yet.
One more thing: your homeowner's insurance typically covers removal of a tree that damaged a structure, regardless of whose yard it grew in. A licensed company will write the invoice the way the adjuster needs to see it.