There's a few, possibly conflicting, considerations. Structurally it's often recommended to run perpendicular to the joists, as mentioned. Normally most of the floor would have joists parallel. Visually they could go either way down the hall, depending on the effect you want. A third consideration is that it looks better if the boards run towards windows, rather than perpendicular to them, especially when using pre-finished wood with microgrooves. If you are doing the entire floor then I recommend you consider each room too. You can have thresholds at each room but I think it is more elegant and "flowing" to have the entire floor as one layout. If that's a design goal then you should consider the entire space together. The photo is of an installation by me where the whole 4-bedroom floor is one continuous flow.