20 online ranked games is not a lot, but if you are looking to get this ASAP I suggest boosting this with a partner while going for several other achievements at the same time.
Keep in mind all of the faction related achievements only require completed games, not wins. However you ultimately need 100 wins so this is what I suggest. You and a partner go in to 1 v 1 match. Unselect the same maps (e.g. the last 4) then search at the same time. If you are doing this together the hope is you get matched up quickly and often. If you are getting matched properly this can go quickly, but if you get randoms it's no big deal, just concede the match and it will still count as a completed game.
Anyway, once you get matched up, have one player concede the match. Search again and have the other player concede. Repeat until you get 20 matches, then move on to another faction. While you are doing this you'll earn the following achievement:
And you'll also make significant progress towards:
Other achievements you can get while working on these:
This involves a bit of luck as you'll need to get matched up with your partner 5 times in a row. Any random match up cannot guarantee a win for you. Keep trying and you should get this. If you keep getting randoms, try off peak hours like early AM or late at night.
Before you just concede each match I suggest going for the 20 champion wins. The quickest way is to have the player conceding capture a victory point then concede. They will lose but be crowned champion. Do this until each player gets 20 champion ratings and then you can switch to just trading off concedes
This is not too hard you just need to get 6 players together. Since this is still ranked I suggest getting this while going for factions, but if you still don't have this after getting all faction wins then it's no big deal.