Mods...please sticky this so we don't keep seeing 10,000 posts about it, then you or I can remove this part from the post. I ask because the former guide that was similar seems to have gone away.
First and foremost, have the patience and time to do this, as it is called a "grind" for a reason.
Upgrade your Feasting Hall as high as you can afford, and Rally Spot to 1 level under this. (example Feasting Hall level 8, Rally Spot Level 7) and hire as many heroes as you can to fill up the Feasting Hall. From my experience, stats do not matter on these heroes for the low level valleys as all heroes I have sent to attack have had roughly the same results on finding medals. Now, make sure you control at least one less valley in your town hall than the town hall's level (have a free valley to be able to conquer).
Next, find the closest level 1-3 valley to you. Don't bother scouting, complete waste of time. I just saw another post asking what a valley is. A valley is anything other than a city on the map. (Swamp, Hill, Desert, Flat, Lake, Grasslands)
For a level 1 valley send 50 archers. Level 2, send 100 archers. Level 3 send 200 archers. Using this method I do not lose any archers at all, if you find yourself losing a few, increase the amounts sent.
Now, the "farming" part. Send an attack on the valley close to you, keep the attack screen open and wait 10-15 seconds(to account for lag or being disconnected)and send the next wave. Do this until all waves have been sent out. Next, open up your map screen and hover over the valley you attacked. Once your first attack lands, click on the valley, choose "enter" and click on abandon. This will send your hero and troops back and instantly regenerate the valley for your next wave of attacks to hit. Repeat this until all of your troops are returning.
Do not expect a miracle. The drop rate is very low, 1% from my experience. You may find 2 medals out of 10 attacks, or you may not find any from 100+ attacks.
Good luck to you all, if you find this guide useful maybe PM a moderator asking them to sticky it for more people who would also find it useful.