Ok from the top.
Choose the city you are going to medal farm from.
Get 250k archers in there and 10 heroes in the feasting.
Make sure you have a valley spot free.
Choose your level 9 valley - preferably 1 mile away.
Send your waves - I use 20k archers 1 pike sword scout cav phract.
Have 10-15 second gaps between each wave.
Each time a wave lands click on the valley and abandon it.
The next wave will conquer the valley, abandon it again.
Repeat until you have RSI or the medals you need.