The process I follow is simple. I go color by color White Blue Black Red Green and for each color complete all combinations. That means White Blue, then White Green, then Blue Red, and so on. Notice I am skipping guilds because I am only applying this process to the the five guilds in RTR. (If you click on an item I have linked the text to the blog post showing those cards):
--Look at your White cards
--Look at your Blue cards
--Add Azorious cards and try a build
--Look at your Green cards
--Add Selesnya cards and try a build
--Look at your Red cards
--Add Izzet cards and try a build
--Look at your Black cards
--Add Rakdos cards and try a build
--Add Golgari cards and try a build
The best build I can come up with with these packs seems to be Selesnya.
Here is a selection of guild-specific pulls from these packs.
Azorious
Selesnya
Izzet
Rakdos
Golgari