Instructions
Click "## Users online" in the top-left corner of the page. Select a user from the list of online users and click "Party." Click an egg in the party and click "Yes, Hold the Egg." This will earn you one credit. Continue doing this for other eggs and users to rack up credits.
Get people to interact with one of your eggs the same way you interact with theirs. After the egg has been held enough times, it will hatch, and you'll earn credits. Adopt more eggs from the Lab and hatch them to continue earning credits.
Purchase a Berry Pouch and Suitcase from the Shop after earning enough credits. Once you have a hatched Pokemon and these two items, click "Farm" and use the Nearby Places section to send your Pokemon on a Scouring Mission. When it returns, it may bring credits. It will also bring back items that you can sell to earn credits.
Post in the PokeFarm forums to earn some credits. Be careful to observe forum rules or you will be banned from the PokeFarm site and won't be able to play.
Refer a friend to the PokeFarm site and have him reference your user name when he signs up. This will earn you 500 credits.