How to visit Teotihuacan while staying in Puebla?
One option to visit Teotjhuacan while you stay in Puebla is taking the Highway to Mexico City and before you enter the city, take the route to Los Reyes - La Paz, Texcoco, Tepexpan (among many other towns). You will reach and "connect" with Teotihuacan highway. Enjoy your visit.
It's simple: you go to the bus station in puebla called CAPU and there you buy a ticket for a trip to Teotihuacan in buses ADO. It's not so expensive and it will take you there and return to Puebla in the same day.