Getting Credit Cards to build credit

[Quincy Gordon Jr.]

Hello BP community, 

I am trying to decide what other credit cards should I get to help build my credit. I have no previous credit history so the mortgage loan officers I've spoken to have said to start building credit and to have at least three lines of credit. 

Currently, I am getting a discover secured card and I am considering getting a Best Buy credit card and then an airline card (I don't know which one yet). 

I don't if I am making the right decision should I just apply for another credit card from another bank? And my last question, how long should I wait before I get each card or that does not matter? 

Thanks for any help