First and foremost I suggest you save your affluent playthrough for this trophy, as it will net you about 4 of them as you go along. First, you must select a "common" officer who doesn't belong to a lord. This means you have to play as one of the generic officers in the game (preferably with an affluent fame type), who you choose is up to you however that is the only real suggestion I can give.
Once you've picked your officer, you must start building your affluent fame to AT LEAST 7 in order to use the special for obtaining the imperial seal. I'd suggest raising your own banner and beginning to take territories on the map, along with making deals with the various supports in order to get materials as you need 99 of each to obtain the seal. Upon reaching level 7 affluent fame, the special will become available to you and if you have the resources you can get the tedious part of the trophy out of the way.
After becoming Emperor, you simply have to unite China in order for your trophy to pop. Personally, I would suggest getting your affluent fame up to 9 so you can reach the maximum fame for that trophy along with obtaining the affluent ending. With this, you should pretty much have everything tied with the affluent fametypes assuming you used the appropriate strategems along the way.