You should know from articles like this or this that you can earn and transfer Avios between Avios.com, British Airways Avios, and Iberia Avios. Each of those programs has pluses and minuses for earning and redemption, making the free transfer feature quite useful.
Aer Lingus will join the Avios world in July with AerClub. On the plus side that should mean their awards will be bookable on BA.com. On the minus side, their flights will probably soon be hit with fuel surcharges when using Avios. They’ll probably also end their award relationship with United.
In the meantime you can pre-register for AerClub Avios and earn 250 Avios when the program launches. With Iberia Avios you need to earn Avios in the Iberia program before you can transfer Avios from British Airways to Iberia, so this can be a good way to activate that feature with Aer Lingus as well. Who knows if they’ll also have discrepancies as large as BA and Iberia have.
Just click here and follow the “not a gold circle member” link where it says you will get 250 Avios for pre-registering. Then scroll down, enter your name and email address, and click send details. In July they’ll presumably email you a link to enroll and earn 250 Avios for doing so.