I have two main concepts for how solos can be created in high level games.
The first is having your competitors have the wrong kind of units and/or have difficulties with builds. There are a bunch of examples of this. For example, as an eastern power, when you stab Germany, often the first centers you take are Munich/Berlin and thus keep Kiel occupied for the rest of the game, stripping Germany of the ability to build. If Germany has a bunch of fleets, all those fleets do is freak out his neighbors. This is why it is often good to go take Munich/Berlin fairly early as a southern power. On the other hand, as a Western power, Warsaw and Moscow are often vulnerable in the late game (especially with some good diplomatic planning ahead) because Russia often has a southern fleet sitting in Sevastopol that gets in the way of defending those centers from an attack from the north. But the obvious example of this is also the most common reason for a solo by France, which I would guess solos twice as much as anyone else, but I don't know that stats. Very, very often France can set up a situation where the whole top of the board is clinched because England/France/Russia don't have enough northern fleets to avoid being overrun. Combine this with the relative ease with which France can hold Tunis, and France has a very clear path to a solo. The two examples I will link to here are both gunboats, but that is just to emphasize that you don't need a silver tongue or anything like that. It's just raw strategy/tactics.
The first example is one of the more breathtaking gunboat performances I have seen, by Babak, one of the best players ever on the site.
gameID=56629 If you look at the board after Autumn 1905, the solo is already essentially clinched when he as France has only 11 centers! The only center that he needs that he might not get is Berlin, and by Autumn 1906, that is clinched too. A beautiful game.
A more extreme example from my own games is
gameID=104961. In this one, I would argue that my solo was virtually clinched (although not as absolutely and clinically as in Babak's game) in Autumn 1911 when I had only 7 (7!) centers. This is because I had broken England's back and Russia was underfleeted with only one more obvious center on the way, and so I was pretty much guaranteed the entire top half of the board except Berlin and Munich. The south was even better, as Austria only had the one original fleet, so it was almost certain that I would eventually get all of Italy. And that's what happened.
The other main concept to help one solo is to use the threat of elimination to get a small power to work with you. In particular, powers are often doomed to be eliminated when the draw contracts unless they get across the stalemate line, and so they can help you break the stalemate line open. And you want to get them working with you as early as possible, ideally when they still have 6 or more centers. The fact that this doesn't happen more often is the number one way that the general quality of games on this site could improve. Early draws are boring. For example, the game that is simultaneously my favorite and my most frustrating is
gameID=15117 where I became an early English vassal of davebishop's France to help him solo, after which I found a way to turn the tide, making him my vassal and leading to me having a clinched solo. He then bamboozled me and I pissed it all away, but nevertheless it was a great game. A very similar example from the World Cup that I didn't screw up is
gameID=81978, which basically has the same thing going on. France faced certain elimination unless they worked with me, which gave me the opening I needed.
It's obviously not just and England/France thing. My favorite live game I have ever played on this site (which has a lot of familiar faces) is
gameID=46844. The key to my solo in that game was leveraging a completely doomed Austria as my ally in 1912 onward to help me break into the west. Otherwise, I had absolutely no chance of soloing.
So I hope that is at least a little bit of insight into ways to break open a game into a solo opportunity.