A safe word is a safe word - or it is meaningless. It STOPS whatever is going on, NOW. As others have commented, there are intermediate (yellow, etc.) ways to communicate.
Since you are new, it is best to move "up" incrementally and then debrief afterward. If you're going to have a mutually satisfying relationship, it has to be built on communication and it is worth the (long) time invested. It doesn't have to be during the "scene" but there are lots of ways to check in with your sub or have him let you know how he's doing, such as taps on a surface, finger snapping, patterned sounds (even if gagged), etc.
This is the most complex part of play. Building your "psychic powers" to read your sub (and for your sub to read you) takes time - time that is well spent if you pay attention. Thinking that you must play a preconceived role, i.e. become a "hard-assed bitch" in order to be Dominant, etc. is evidence that you need to learn more before you become too aggressive. Safety first - and second - and third.
Communicate before, during (as noted) and, especially, after. And, pay attention. The responsibilities are great for both of you, but for you, most of all.