Any detailed advice or videos you can provide to help with this? Something other than just 'improve footwork'?
Isn't that basically it though, lateral movement? You can use it when not cutting off the ring, to get back in the centre of the ring, or when you're being cut off yourself. The idea is pretty simple, he'll move to the side to get off the ropes, you'll have to move with him and anticipate his movement to make sure he can't do that.
Make sure your movement uses the right fundamental movements (assuming orthodox); left/forward= left/front foot first, right/back = right/back foot first. A lot of people assume they have this down, including myself, only to look at a tape and spot a few bad moments of foot placement. Lots of pressure fighters like Tyson, JCC, etc. are known for cutting the ring off quite well, but I think a good example for someone trying to pick up easy tips would be the first 6 rounds of Cotto-Foreman. Foreman isn't the best mover, but he is dependent on his ring generalship, and Cotto was able to control the distance and track where he was going, often getting there even before Yuri himself did.
It's exactly what it sounds like. Trap that mother****er. Doesn't have to be pretty or complicated. Two really simplistic examples are Katsidis/Mitchell and Wolak/Foreman. A relatively crude fighter just chases a relatively polished and quick boxer down. Katsidis at times literally ran to keep up with Mitchell. Remember it doesn't have to be pretty. There are little subtle ways to do it but at the core it's just chasing a dude and being persistent.
I've heard Tyson say that the best way to cut somebody off is to move the opposite direction of how they're circling. Take that for what you will.
Cutting off the ring? The key is to be aware of your opponent and where he is in the ring. Many of the "rules" of Boxing an opponent are actually backward when walking a guy down. If you don't realize that you are lost. Jab. Jab often. Lots of guys forget it. If he isn't worried about defense his brain is 100% focused on footwork. Use the jab to mask your closing. Always keep his back to the rope! I know this shouldn't need to be said, but many guys pressure by following the opponent. If the guy is a Pure Boxer and you give him ANY way to get back to center? He will. Even if that means kicking out his back foot and pivoting on his lead. ALWAYS only leave him an option of left, right... ALONG THE ROPES or back! Shorter choppy steps when closing the last steps because you must be ready at any moment to slide left or right and "pinch" off an escape route. You want your feet in contact with the ground because as you close the noose his strides will need to lengthen to take advantage of escape routes. You need to be ready and able to mirror his movements AND gobble up his feints. Close and circle slightly TOWARDS his power hand (or best punch). Yeah sounds wrong, but if you are walking him down? You don't respect his power anyway or you are willing to meet it. OK, with that said, Boxers tend to circle toward their power hand as lifting the front foot kills the offense. His only choices should be bad, circle into you with a muffled power shot, or worse, lift his front foot to step out, and worst (unless he is slick), lift his rear foot an spin backwards (last sequence of check hook). In every case you are expecting it so you can nullify it right when it starts and be there waiting for him. Keep CLOSE even if he escapes. Jog after his ass to get the process going again. Never let his mind rest. He won't panic until that rear foot is 1-2 feet from the rope. Make sure that most of the fight is either there or with you on top of him. After a while his brain will be on fire with just the footwork. Offense? Defense? He's overwhelmed! Remember, jog slightly toward the center of the ring to keep his back facing the ropes not really "after", as in following, him. For you personally... STAY DEFENSIVE MINDED!!!! Closing in on a guy and the prospect of putting the hurt on him can become so engaging you forget that YOUR defense can become porous. Uppercuts, lead hooks, and hooks off of foot feints can put you on ***** street. Stay alert. Watch for the rear foot bounce fake. This is where a guy steps shallow in one direction, bounces off of that foot, and steps REALLY wide in the opposite direction. If that wide step is to the center? All your hard work down the drain. Watch for skipping along the ropes. This goes back to circling towards his power hand. Guys can make a quick escape by dropping back, squaring up (getting thin), and skipping along the ropes (See Andre Dirrell). Hard to muffle, but it is costly energy wise so good for you. That is where jogging to the center after his ass to restart the process comes in. Good luck and make them pay!