If you want a rules-light, cinematic game, use the rules for Basic Abstract Difficulty (BAD) from
GURPS Action 2: Exploits. This reduces the number of fiddly modifiers you need to worry about during play. Although BAD was created for games simulating modern-day action movies, it works well for all genres. For example, I would recommend using it in Dungeon Fantasy games.
I'd second the opinion that
How to be a GURPS GM is an important resource.
I'd also recommend modest initial point totals for the campaign. If you have players who aren't familiar with the system, limit the amount they need to worry about for the first few sessions.