iPhone 6s not syncing properly

I recently got a new iPhone 6s. I synced everything from my iCloud account, but some things aren’t syncing properly. I want everything that was on my iPad on my iPhone, but some things have synced and others have not.

On iMessage, messages have synced over except for one person, where several messages haven’t synced and messages are not receiving properly on the iPhone, only on the iPad.

On calendars, most events have synced over except for several events.

This problem is also there in other programs such as photos and reminders.

How can I fix this?