The narrative technique in Blade Runner is pretty straightforward—although the producers still wanted a voiceover track to explain what was going on. There are basically two main arcs in the story: we get to see what the replicants are doing in different sequences involving Leon, Roy, and Pris, and we also get to see Deckard as he tracks them. Their strands converge and diverge at different points.
For instance, we see Leon alone at the beginning getting interrogated, and then we see him later on with Roy. After that, Leon ends up entering Deckard's storyline (and dying in the process), although Deckard still hasn't encountered Roy yet. Similarly, Pris starts off alone and hangs out with J. F. Sebastian before she eventually reunites with Roy. Roy's and Pris's storylines calamitously converge with Deckard's for the movie's climax.