https://www.youtube.com/watch?v=HGtPF_13AaA Best video that comes to mind. Covers just about everything. Against an aggressive falco, I'll usually let him approach since I'm pretty confident in my defense against lasers. Depending on the range, my go-to options are SH oos fair, or wd oos. Short hop fair is best when you tipper it, because then it resets back to neutral in a position that favors you, or sets up for a grab while hes still airborne (usually around 30-50%ish). If he goes in at that range, dash-back grab is good for marth reasons. If he goes for another laser, you have plenty of options. If he goes back and lasers, a dash attack might be good. If he stays in place and lasers, your f-smash has a good chance of tippering.
But say a falco gets on top of my shield. At this point all you can really do is roll, get grabbed and DI it, or find some other niche hole in his pressure.
Platforms are also pretty key against falco, especially a campy one. If a falco laser camps, you can try to get to the top platform, or use platforms to let you jump towards him. You can also waveland on a platform if he gets near you and try to run back to center stage.
Something that has helped me SOOO much against falco is the idea that you only want to hold shield in anticipatio/reaction of lasers. I know this sounds obvious, but my gameplan against falco used to be to sit in shield for 65% of the neutral, and use basic oos options to beat scrubby falco neutral. A lot of falcos at a low level actually have a pretty terrible neutral thats bandaided by lasers, a decent punish, and a lot of smash attacks on shield. So if you learn their patterns, you can punish hard. If they always go in, swat them away or find a reliable defensive option (maybe they just flowchart in and a roll-fsmash will catch them a lot). If they try to laser at a close range, especially near the edge of the stage, an f-smash will do you wonders. You might get a few falcos calling you scrubby for "randy f-smashing them", but don't be discouraged and just realize that you're beating their scrubby option with a read. Back to reactively shielding, you can DD grab a lot of scrubby falco dair approaches. Maybe they spotdodge shine if they miss, but just read this and react accordingly. Just focus on beating scrubby falco neutral options, and then you'll realize what a good falco neutral looks like and you'll be set to learn how to beat that. Thats my thought process on it.
If you get falco in shield, you can literally wait a few steps outside and wait for him to do something, or pressure with d-tilt or some spaced aerial.. He's terrible in shield.