When composing any image involving straight lines my usual approach is to use the edges of the frame itself to determine the alignment of the lines inside it. This means deciding which line will make the most sense as the “horizon” when the actual horizon isn’t available.
When the horizon is present then the decision becomes whether it makes more sense to the narrative I’m trying to convey for the horizon to be straight relative to the frame, or if any other line makes more sense.Usually, for me, the longest line in the frame makes the most sense to be aligned to the edge of the frame.
I tend to stand as opposite to my subject as possible for front-on compositions, but sometimes that simply isn’t possible. When lines curve towards or away from me it can be difficult, but I always try to find elements in the composition that can become the line structure which works for me.
Lines can indicate the way work is intended to be viewed, and can also help draw the eye across the frame. By using lines as structure it helps to layer out elements, almost causing a “stacked” effect, with different aspects of the composition holding different levels of significance depending on how they relate to the main line.
I think that my rangefinder cameras make it much easier to line things up than an SLR or EVF, although I’m not entirely sure why that is; it may just be a way I use them. The frame-lines being separate from the rest of the viewfinder may be a factor.