At some point you will need lots and lots of medals to get rank and get a promotion. For that you need to go Medal farmin.
First of all you have to choose where to farm, the spot/valley depends on what medals you want. To take a look at
this guide and pick a valley. For Rose Medals the best place is a Lake.
Remember though, the higher level of valley the better chance of getting a medal. But its still not easy to get them, for Rose Medals I had to attack 10-15 times to get the medal I wanted.
Besides medals you will also gain items.
Another thing to think about is that
you should have already counquered max vallyes that you can hold; the point here is to attack the valley over and over again with out taking it. Amount of valleys you can hold is the same as your level of the Town Hall, if its L4 then you can hold max 4 valleys.
Take a look at your map and choose the best valley for you to attack. Note: the valley that you are about to farm cannot be owned by another player.
Now send your army as normal, this way you will
kill all the military there and their Hero. To be sure that you killed all the defenders attack as normal again, if everything has been done correctly there wont be any fight since there will be no defenders. Thats all in order.
Now
send an army of 20-50 or more scouts*, dont scout but attack. Scouts are fast units and they can attack and come back within minutes. If you have a Rally Spot of L5 and Feasting Hall of L6 then get 5 Heroes for this. And send them all at once, over and over again. I did 5 wave attacks every 2 minutes.
If you do it over and over again the valleys army wont be able to respawn and you can farm whole day with out meeting any resistance, or untill somebody grabs the valley in question. Note: I think that the respawn rate for NPC defenders is 30 minutes.
In just few hours you can aquire enough medals for your satisfaction, here is a screenie of me farming for couple of hours.
* If the enemy is regenerating then you need to send more scouts to opress them enough.