There are some interpreters today who suggest that Luke and Acts should be separated. But I truly believe in the importance of hyphenating Luke-Acts. There are numerous, significant, and meaningful links between Luke and Acts. In this vein, see these two posts (here and here) from Michael Barber summarizing an article by Charles Talbert on these thematic links. By the way I would add prayer to the six themes noted. You might also want to see this earlier post.