The Mat Pimp -
To me, the hard part is getting people into closed guard, especially with so many people passing standing now. Once they're in my closed guard, keeping them is relatively easy because I can act, they can only react.
This is very, very true especially at black belt comp level. I've been watching a ton of Kron to research closed guard, and concluded that even he doesn't have an easy time getting and staying there.
IMO the best, best way to get to closed guard against a standing opponent is to (like Kron) play a good old collar-sleeve from open. This is not an easy guard to play, since it requires you to maintain very specific foot placement (hip and bicep) against opponents that are much more mobile than the guard player. There are plenty of tips online on how to break people down to their knees, but the guard player has to be more active in trying to off-balance. It's not hard for the top player to just deny you foot placement without actually trying to pass.
On the other hand, there are a few Roger Gracie videos on YT showing how he breaks closed guard by standing. IMO it's extremely effective. I used to wreck lots of my students in closed guard but since I started teaching them the underlying objectives Roger taught and how to pass that way they've been making it far less easy for me.