The Jannah we are all aiming for is slightly different from the Jannah Adam(as) and Iblis were in. The location might have been the same, but certainly the rulings were not. For in the Eternal Jannah, all it's inhabitants are pure, sinning is impossible, there are no trails in it. The Jannah that Adam(as) and Iblis were in - all of these existed. Iblis always had pride in some corner of his heart it only showed up in the test/trail of prostrating to Adam(as), also Adam(as) was tested and he sinned.
It is clear that they were both in a state of trail, they both had the honor of choice. Both failed in their test, the command from Allah to not eat from the tree for Adam and the command for Iblis to prostrate. While Adam(as) chose to accept his mistake and seek Allah's forgiveness, Iblis chose to persists in rebelling against Allah.
So the Jannah they were in was in this regard different from the Eternal Jannah we are all aiming for. In the Eternal Jannah, all it's inhabitants will be completely purified before they enter it. Inside it there will be no more trails, no more prohibitions, no more evil, no more sins, no more ignoble qualities such as pride, envy. In the Eternal Jannah the one he enters can never be expelled from it, it is pure and its inhabitants are pure. All are in a perfect state of Felicity and Gratitude.
Gratitude is the key ingredient, everyone in the Eternal Jannah will be completely grateful to the blessings and mercy Allah swt will give them. Whether they are in the lowest rank in Jannah or the highest, they are completely content and satisfied.
[FONT=me_quran]وَآخِرُ دَعْوَاهُمْ أَنِ الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ[/FONT]
And the last of their call will be, "Praise to Allah , Lord of the worlds!" [Quran 10:10]