Earthshaker is a super fun support because his playstyle is very different than most heroes, and most importantly he has the ability to completely swing teamfights in your team's advantage.
You should do a lot of pulling in the early game to get a few levels, and also very importantly you should roam to lanes where a long ranged stun can make a kill difference, and sometimes sit behind allies you expect to get ganked.
Build either a Soul Ring or an Arcane boots, and afterwards farm for Blink dagger. Make sure to minimize your deaths as that's the biggest way to delay your Blink Dagger.
Try to pick Earthshaker against lower hp heroes that don't want to be stunned. He's not very good against super tanky heroes since his damage combo only does so much.