Measure floor to ceiling along points for the hang - sometimes the suspended ceiling drops by 5-10mm or the floor / skirting isn't straight. Assuming straight, put + laser in centre and mark with a very fine point spirit marker on tape. Mark height on far L&R of install, on tape as well, so if you need to move the laser, you have a set height further down the corridor.
If you can swing the depth of a bubble level as the spacing, then take a very fine point spirit marker (I like the write 4 all's) and draw the spacing between prints, and the size of a print on the level (use a t-square to make sure the line on the level is perpendicular all round).
If not, then cut spacers from 5mm pvc, and mark those up. Place centre print, then work out on the horizontal. Spacer below, work outwards. Spacer above, rinse and repeat.
If you're fixing subplates, then line them up the same way.
Laser is there for sanity check.
Clean off spirit marker maks from spirit level at end of job, with IPA or lighter fluid.
I've hung far too many exhibitions.