The Aston Villa captain has shone in the Premier League this season, sparking rumours he could be set for a big money move to champions Manchester City.
Southgate had initially appeared reticent to calling up Grealish, delaying his international debut until September.
But the 25-year-old revealed he had an hour-long meeting with the England boss during that first camp to explain how to take his game to the next level.
"He's the manager of England so he's obviously going to be a brilliant coach. He's helped my game massively," Grealish said on Wednesday.
"At the start of the season I said to him 'what can I improve'. I'm not going to go into too much detail as what we spoke about, but he gave me a few things to work on to try and force my way. I think it's worked, because obviously I've had seven (England) games since."