Spacing spacing spacing. This can be a difficult match and you have to control the tempo or Marth can and most likely will get the upper hand.
Lasers and Phantasm are very helpful. One allows you to control the game from afar, and the other lets you get out of pressure (fairly) effectively most of the time.
Shine might seem like a good move to use for spacing, but don't abuse it. If they start predicting and powershielding it, it can lead into a tip. Use it sparingly.
Be careful trying to take Marth on in close range. If you have to, stick really close and use your jabs and tilts until you can get out. The air is also not a very safe place for Falco to be in due to him being outranged by Marth's aerials.
In general, just keep your distance and wait for the Marth player to slip up and then exploit their mistake. This is all from my own experience, so take that as you will.
Definitely do not "roll and smash". Marth will punish you, I guarantee it.