RE: Why you shouldn't be sad when you get common reward cards!

The summoners are the core of your team and it's the only cards that you can't really earn. You need to buy them. Either with your ingame earnings or with external money. The best is to actually start to develop one summoner to level 2. This will allow you to play cards of this level for this splinter if you are in bronze league at least.

This is the best way to progress. The next step is then to develop another splinter to level 2 and little by little develop your team.