This is based off your league popularity and your stats. After game press conferences will get you your League wide popularity. Answering with A (professional) B (arrogance) to all media questions will net you the most popularity, however Answering with arrogance can lower team chemistry and/or fan support. Donating to a Charity through my purchases with also net you an additional 5 to popularity.(Can donate once per year)
As for stats, Try to be in the top 3 in 2-3 different categories at your position.
The All-Star game is in February so this will take you around 50-55 games to get to it.
(I've read a lot of the forums that this achievement doesn't seem to be unlocking for people. It does not matter if you sim past the All-Star game or if you are a starter or not. The achievement should unlock when you are selected to the all-star game.
I recommend you make a duplicate save in mid Jan-Feb in case this is glitchy.)