Firstly just handle the snake a bit is startling but not dreadfully harmful or really painful. They are not typically biters so don't worry just move slowly. Wear a glove if you are really concerned.
The clues to determine what the snake is doing are very subtle but are there. They have two modes of behaviour, instinct and conscious. Instinct is response to feeding and or breeding or attack. If you are careful about keeping your self rat smell free and you are simply to big to eat until you make a mistake or the snake misses it will not mistake you for food. You will never smell enough like a sexual partner for your snake to make that mistake.
Most of the behaviour of your snake and you will be conscious on the snakes part. So lets look at some clues.
Breathing, yup it is hard to see. They do move the rids to breath so if you watch you will see it. The problem is you need to know what normal is watch the opening of the hide and sooner or later the lung will be up along the opening and you will be able to see how fast they breath when relaxed. Small animals is a bit faster that I do and larger slower but that is me and mine everybody and every snake is different.
The faster the animal breaths the more fear/stress ect. it is feeling. (lets ignore everything else fear/stress - feeding/sex that is it) It is a bit of a gauge.
The tension in the body area that is not moving is also a indication more tension more fear/stress Remember that is for non moving parts.
Tongue, the easiest 'tell'. The tongue is a very important sensory organ of the animal, a fearful snake under great stress or great fear will is not interested in the environment just in being still you will see little to no tongue flicks. A flicking snake is interested in what is surrounding it and is 'curious' if you can apply that term.
snake see very well they not only have colour vision (less that human) and it is believed to be tuned to movement but they also have heat pits with are connected to the optical lobe of the brain so they see heat as well. You snake tracking your movement it is just watching you.
Remember this it is much more important than it may seem on the surface. Snakes (in general Royals in particular) want to watch you and not be seen doing it.
They ambush predators and want to watch and not be seen it is just the way they work. They need hides (so they can hide from prying eyes but can peek out and watch) the like to have cover (overhead and or ground cover) so they can't be seen from over head (birds are a big time predator of Royals) Every aspect of they life surrounds "see but not be seen" mentality.
I hope this helps, don't be afraid just move slowly and touch the sides gently so your snakes knows you aren't going to eat him and so you can calm your nerves. If will be fine just be slow stay away from his head.
Hope this helps,
Alex