The easiest way to get to LA is to fly into LAX or Burbank airport. Both airports are serviced by most major airlines in the USA. You can drive to LA from other parts of California but those who live further away a flight into the city will make the most sense.
From LAX airport you can take the US2LAX bus to the city's main Metro station. The Gold Line will then take you to Pasadena Station. There are free shuttle buses from there to the stadium. If you're taking public transport from your hotel, take a bus or the Metro line to the main Metro Station and follow the same directions above on the Gold Line.
Like most LA natives, you can also drive to the Rose Bowl stadium. There is very limited parking available on a first come, first serve basis. Parking spaces can be booked at the Parson's Garage which is a few blocks from the stadium and offers a free shuttle to the stadium entrance.