You cannot get ahead in this game on your own. You will need allies. Even the kings need the voluntary support of most their subjects. Your principle ally is your king, or, if you are a king, your subjects. Find your king and pledge fealty to him. Then try to remain loyal. The next most likely allies are players with fiefs near your own. Find out who they are and try to work out some kind of alliance. Try to befriend everyone, even your enemies and inlaws. Friends when you need them is the key to winning the game.
Each game often has one group of players in France and England who seem to dominate the play. This gives rise to complaints of 'the same group of players being in charge, getting the big positions and making decisions. This perception is not accurate, although it's a common one on the part of players in any game who find it frustrating that they're not part of "the group." In any game you will find a group of dominant players who have a great influence on things. The way to join that 'elite group' is to know what you're doing and just do it. Play successfully, or even just energetically, and get the respect of the other players. One becomes influential through one's own efforts.
Being one of the dominant players here has nothing to do with the size and rank of one's starting position. There have been as many or even more influential players playing from small positions as there have from large ones, and there have been just as many large, rich positions whose players just sat on the sidelines or went inactive. Look around once the game is underway and you will see several examples. Many of the players most active and successful in every war so far have had small positions. The dominant players in the game are those who play smart and make the most of their position. There is nothing to stop anyone from doing that. If someone doesn't like their position, they can, as was pointed out, go inactive and try again. Also you can get in touch with someone who has a coveted spot that seems to be going inactive or sitting unplayed, and ask them to switch. Don't forget that players can switch positions if both agree. Usually, someone who's not playing anymore doesn't mind doing this.
Unfortunately the problem with some players often seems to come down to "I can't do whatever I want cause the other players don't like it." The smart and successful players here tend to see the importance of having a civilized society with rules of behavior, and will oppose attempts to reduce it to anarchy. That's quite realistic, and it's also up to the players. Nothing stops anyone from opposing the "will of the majority" here, but you have to expect to take the consequences. If people want to do whatever they want to without reaction from the other players, no one can help you. What players have to keep in mind is that the game doesn't prohibit any In Character actions, and enforcement is up to the players. But just as the game doesn't keep them from doing what they want, it also does not keep the other players from not liking it and doing what THEY want in return. There are no gamemasters in HYW. Some people want not just the freedom to do what they want, but a moral judgment handed down that it's OK and nobody should complain. That's not the way it is. Anything is OK by the rules of the game, but no one can control whether it is OK by the other players. Even the Heralds' influence has little effect on this. The Heralds do not demand chivalrous behavior of people. What Heralds will do is explain the situation and the options, and it's not always a pretty story. If players don't like the situation, that is something Heralds can't help with. You can try appealing to the game's Sysop, but the Sysop is there to enforce the rules, not to judge what is done within the limits of those rules.
Be warned that you are likely to get very wrapped up in your character. This was the case during the earlier testing of the game. All the player characters in the game are historical, as are some of the non-player characters. If you know anything about the history of this period, you will recognize them.
How to Taunt Your Opponents