This fairly straightforward to get. All you have to do is have 2 color sets of properties. Example:
3 red color properties (Illinois Avenue, Indiana Avenue and Kentucky Avenue) and having all
3 yellow properties. (Marvin Gardens, Ventnor Avenue, and Atlantic Avenue) Buy for each property the required 4 houses and then upgrade each to hotel. After the final hotel is placed the achievement will pop.
This just an example of what you can do to unlock the achievement. Any color set will work as long as you can place house and hotels on it. So Railroads and Utility companies will not
work in obtaining this achievement!
A method to use to obtain this achievement quick and easy would be to have local player match set up. Have same controler for all selected. Add up 6 non-AI players. I recomend that you have 6 players if you have not gotten
However you will need to at least have added 1 other non-AI player for this to work. After you have the game started with your number of players chosen. Have the players that are not you trade you all their money and you trade them 1$. This is so you can afford the properties, houses and hotels easly. After you are done trading with yourself bankrupt all but 1 other player. Play the game until you can obtain 2 solid sets of properties. Once you have gotten the 2 color sets, go to work on building the house until you can place hotels on each. When the finale hotel is place the achievement will pop.
If you did select 6 players for this achievement play through, then bankrupt the final player. This will cause the game to end with you winning. The achievement for Champion will pop right then and there.
Best of luck to your achievement hunting!