Flooring – Which way do you run hardwood flooring to make the room look bigger

First, remember to lay your wood perpendicular to the floor joists. Laying it parallel can cause a waving effect which is unpleasant.

Next, find the longest, longest, straightest wall which is perpendicular to the joists. Measure out two feet from the wall all the way down the wall. Then find the best line down these marks, snap a chalk line, Measure back to the wall about 23 and 5/8 inches. Snap a this line. Line up your first run of floor against this line, tongue side out (nail through the tongue).

As for room to room, if they are really out of square with each other, try building a transition between rooms:

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This allows you to lay each room separately, allowing each room to be square.

I'd like to write an answer on the overall methodology on how to pick where to align a floor, but I don't have the chops for that. But in your case, I do have a suggestion.

One of the principles of flooring installation is that it's more important to look straight than to actually be straight. For example, you have that architectural detail separating the two rooms. I think it would look more odd if the flooring did not line up with that detail than if you had a wedge shaped piece against a wall. Snap a chalk line down the middle, measure from that line to within a few inches of the starting wall, and snap a second line parallel to the first. Align your first piece with the second line. Then every couple of rows, measure to make sure you are still parallel with the first chalk line.

An alternative would be to snap the first chalk like as I described above and start from the middle of the room(s) and work your way out. Depending on the type of tongue and groove and nailing method, this may not be possible.