Well, a good place to start is by looking up online guides or discussions from fellow fans. They often provide clear indications of where to pick up the manga after the anime. Another option is to check the official My Hero Academia websites or social media pages for any recommendations.
The best place to start the MHA manga is from the very beginning. It gives you all the background details and builds up the story nicely. You won't miss out on any crucial developments that way.
The My Hero Academia anime is pretty much in line with the manga. It keeps the main story beats and character arcs intact. Though there may be some additions or omissions for the sake of pacing and visual presentation, the essence of the manga is well-preserved.