The first sequence of your screenplay is the most important part of the written script. Remember, the reader is looking for any excuse NOT TO READ, so you must grab her attention full throttle and get her turning pages quick. There are a few exceptions, but for the great majority of screenplays you only have about 12 to 15 pages to do this, depending on the genre, and there is a lot to accomplish in those precious beginning pages:
(1) Establish TONE, do it quick and early. Be consistent. (2) Establish your PROTAGONIST, and he/she must be interesting and empathetic, with clearly defined flaws. It is not essential for the main character to be likable or sympathetic, but it always helps. (3) Establish the WORLD OF THE STORY (and any World RULES that go along with it). (4) Establish the STATUS QUO of your central character’s life. (5) Set up the DRAMATIC PREMISE of the story. (5) Usually ending with the INCITING INCIDENT, although this first major plot point can sometimes appear earlier in the sequence.