The Mishna in Sanhedrin, which we say before Pirkei Avos, tells us, "Kol Yisroel Yesh Lahem Cheilek L'Olam Haba", every Jew has a portion in the world to come. However we find many times Chazal tell us that certain people do not have a cheilek in Olam Haba.
The Yeina Shel Torah brings from the Chofetz Chaim that in this instance the word "Cheilek" means a lot of land, "Chelkas Adama". Every Yehudi is given a barren field and sent to this world to work on it. He must plow it and care for it and nurture it until it yields beautiful fruit. The harder you work the better the results.
This field is your cheilek in Olam Haba. If you sit by idly and do not tend it or worse yet you destroy it but pouring on it toxic chemicals, that too will be your cheilek in Olam Haba. Once you get there though, there will be no opportunity for any improvements.