TL(Wont)R: Get partner, start 1v1 game with low world hostility, have them concede game after 15minute mark (June in 801).
This and all "50 wins with clan X" are best done (or completed) with a partner to boost with. I want to note, this is the absolute least fun method you can use to play this game. This is a great RTS with a unique spin on the genre and tons of customization to it. I would advise getting a lot of manual enjoyment out of it first. Perhaps go through each clan's conquest to get those achievements, and if there are clans you enjoy, go for their 50 wins naturally.
That said, again, this is done the fastest with a boosting partner. As of the time of this writing you only need to be in a game for 15 minutes for it to count as a win. Start a game with just you two, and low world hostility. The person getting a win is the only one who needs to select a clan if they are going for 50 wins at the same time. Once past the 15 minute mark (once you see June or later in year 801), the partner can concede the game. As long as those 15 minutes have gone by, you will have a win. If trading directly with your partner, that makes it about 31 - 32 minutes for you to both have a win with your chosen clan. If you are both pros can you likely do a 2v2 vs comps in that time and get a normal win that is more enjoyable. If doing it boosting you can pretty much walk away for those 15 minutes. Low world hostility means only a couple wolves will attack your starting tile in that time, and your six villagers can handle that just fine. Your time usage can be cut in half if you have access to a second computer and somebody's shared library. Since then you are only getting those wins for yourself, meaning a win every 16 minutes. Provided the other person doesn't care about their "time played". Note: If done around Christmas, each player will likely earn the Make a Snowman achievement, so if that will mess up somebody's tracking, keep that in mind.
SECONDARY METHOD: Start up a multiplayer game with you, one easy computer on the other team, and as many Expert computers on your team as you feel like (depending on map size). Once started you can walk away. Comps seem to win almost all games before something ruins you. Avg time per win roughly 55minutes. Most likely to fail by you dying to spectral warrior event if it happens before your team wins.