Car: Use google maps.
Train: Amtrak comes directly to Niagara Falls and from the station you can walk (1 mile) or take a taxi for about $6.
Bus: Major bus lines, such as Greyhound and Megabus, go to Buffalo. From Buffalo you can take the NFTA bus to Niagara Falls. During the summer season, Greyhound runs to Niagara Falls.
The local bus line is run by Niagara Frontier Transit Authority. The closest stop is a block away on the corner of Lewiston Road and Garrett Ave.
Plane: If you arrive by plane into Buffalo Niagara International Airport, you have 4 options to get to Niagara Falls, from most expensive to least expensive:
taxi, UBER or Lyft, ITA shuttle, NFTA bus.