1. Being pious in every act we do and every word we say.
2. Remembering the fact that our Imam Al-Mahdi (AS) is alive and he is informed about our acts and deeds and trying to always please him by obeying Allah (SWT).
3. Doing more good deeds and gifting the reward to Imam Al-Mahdi (AS). Pious believers gift all their reward to Imam Al-Mahdi (AS) and other Infallible.
4. Praying sincerely for Imam Al-Mahdi (AS)'s reappearance and keeping it as our first and upmost important need.
5. Preparing ourselves to serve our Imam (AS) in every possible way that we can including serving his followers and lovers and spreading his message to people.
And many other noble acts which can help us in this regard.
Dajjal or Antichrist will be before the reappearance of Imam Al-Mahdi (AS) and he will be killed by Imam Al-Mahdi(AS) or by Prophet Easa (Jesus) by order of the Imam Al-Mahdi (AS).