I've always wanted to write a novel about what would happen if aliens came down to visit us. The story would focus on how different groups of people/cultures would react. Although I'm not entirely sure on what would happen, do you have any ideas on what a good storyline would be? Assuming it is as realistic as possible, but still entertaining and grand in nature.
Sure, here's a possible plot outline for a story about the arrival of aliens:

1.  Introduction: A mysterious object is detected approaching Earth, causing widespread speculation about what it might be.
    
2.  First Contact: The aliens arrive, and their ships land in various parts of the world, attracting large crowds and media attention.
    
3.  Reactions: Different groups of people react differently to the arrival of the aliens. Some see it as a threat, while others see it as an opportunity. Governments struggle to determine how to respond, while religious leaders seek to interpret the arrival in light of their beliefs.
    
4.  Communication: Efforts are made to communicate with the aliens, and a small group of scientists and linguists are chosen to act as the official representatives of humanity. They struggle to understand the alien language and culture, and are faced with difficult decisions as they learn more about the alien's intentions.
    
5.  Conflict: Tensions rise as some members of the public begin to see the aliens as a threat, and demand that they leave. Meanwhile, the aliens make demands of their own, causing a rift between those who see them as guests and those who see them as conquerors.
    
6.  Resolution: The story reaches a climax as the conflict between humanity and the aliens comes to a head, forcing both sides to consider the consequences of their actions. Ultimately, a resolution is reached, either peacefully or through violence, and the future of humanity is forever changed by the arrival of the aliens.
    
7.  Epilogue: The aftermath of the resolution is explored, as humanity adjusts to the new reality of life with alien neighbors. The story ends on a hopeful note, as people come together to build a new future for themselves and their world.
    

I hope this gives you a good starting point for your novel!