I've been telling all my friends, family members and coworkers to go see STID. I want the movie to be as big a success as it can be and I know every little bit helps. So I implore you my friends on this board to spread the gospel of Trek and encourage those you know to go see the movie.
Iron Man 3 and Gatsby are strong competition atm, and with another Hangover movie coming out next week things will get tougher. While Hangover 2 was the exact same movie as Hangover 1, they both made $500 million. People would spend money on garbage they've seen before. Just look at how Kung Fu Panda 2 did when it competed against Hangover 2.
Most of the people I've encountered who were resistent about seeing the movie lobbed they think it's nerdy or couldn't get into it back in the 90's when it was on UPN. I sell it to them as Mission Impossible meets Star Trek. It's totally worth the price of admission. Use what other tactics you think could sway non-trekkers.