Oh dear... I sense trouble on the line ahead...
Welcome to the forum. I hope your first post was Tongue in Cheek and set to provoke a reaction...

In all seriousness, I recall someone on this forum saying that a member of staff made them move to their reserved seat (and threw someone who was in said reserved seat out of it)... Tried a quick search but can't find the exact post or I would have quoted it here...
I wish you the best of luck with your new job. As others have said, although I will be a little more realistic, You are going to need it if you have this attitude... Trying to 'enforce' these things is going to make a misery of your day... There is this dreadful term called a "power trip" where someone in a position of authority uses said authority to feel superior to others... It is not a good thing and won't lead to happy employment... Of the
RPIs▸ I've encountered I'd say 0% try this sort of tactic...
Without telling you how to do your job; I am going to instead suggest you converse your efforts to those who knowingly sit in First Class and say "We'll move if / when challenged." Or those who hog the toilets to dodge the fare when someone with a medical condition is stood outside getting increasingly red faced with pain from waiting... Or those who pretend they've made an honest mistake when passengers have seen them claim this "mistake" several times over...
Maybe after that you should try and build a rapport with your regular passengers... They are probably fed up with some of the chancers as above and would willingly provide you details of where/when to find them

Back to tongue in cheek... If you decide to go down the road of trying to enforce silly things then here is a list you can write me up for in advance...
- Soiling the railway. I use the train toilets... ALOT...
I spill my drinks... ALOT... 
- Existing in the wrong class of accommodation from that held on the ticket... I like to visit the Buffet Car for my complimentary drinks... I often use the toilets which sometimes are only available in Standard Class... Finally I occasionally sit with my friends in Standard Class when I hold a First Class ticket... Occasionally I've been moved back to First Class and told my friends can join me...

- Using any article to reproduce sound... It helps to talk to staff when ordering drinks in the Buffet Car or asking for an additional ticket etc etc
- Using the wrong train for a "Booked train only" ticket... Bristol - Newcastle on a train with no working toilets? Not happening!
- Sat in an Aisle Seat when reservation is for a Window Seat? Also not happening!
Finally... Can you please advise me what I should do if my Advance Ticket states Coach * Seat *** and how/where I should sit?