If you mean the daily PVP, it helps to selectively attack weaker players, and to go after players who don't put their good generals on their defense team. Unless you're trying to get the kizuna from the arena missions, it's generally best to focus more on making sure you win all ten matches for the gold tickets than on getting as high of a rank as possible. I personally tend to pick someone I can beat and then beat him ten times in a row--and it's probably been months since I lost an attack I initiated in the daily PVP.
The thing to remember about daily PVP ranks is that whether the player cares about being high-ranked makes about as big of a difference as how strong the player is. For example, Vermillion is currently ranked #44 on the ladder in spite of being one of only four players on the server to have completely cleared the campaign. Zantetsuken is ranked #304, even though he's only of only 13 players to have access to the best endgame campaign farming for cursed shards. I guarantee you that both of them could be ranked higher if they cared to. But I also guarantee you that Zantetsuken has a very easy time getting his ten daily wins for gold tickets.
If your rank is much higher than justified by how strong your generals are, you also make yourself a target for other players to pick on looking for easy wins. That doesn't necessarily hurt you very much, as if someone beats you ten times in a row, then probably at least nine of them were with him ranked above you, so you don't lose further ranking.
It also makes a difference whether you mostly put your best generals on your defense team, especially overnight, to try to fend off challengers, or whether you leave your spare parts on the defense team without swapping your best generals in there.
If you mean that you have a hard time beating top ten players in the weekly tournament, then yeah, that's how it goes. There is some degree of randomness, as well as a rock/paper/scissors element to it in which matchups really matter. That's why it's not just the same daimyo every week. For example, I might be the only player on the server who can pretty reliably beat Aargaez if I build for it, but I'll tend to lose to EarthCrimson, even though there are probably 6-10 or so other players who would beat him more often than not.