I am arriving at Tianjin on 24th April what is the best way to visit the Great Wall?

The closest section is Huangyaguan. I suggest you take bus no. 188 at the front square of Tianjin Railway Station to get to Jixian County firstly. It takes around 2h and costs CNY35. Then you can charter a car or van with other travelers to the Wall within half an hour at a cost of CNY15 or so.