Your job as marth is to use your range, priority, and speed to keep people at the tip of your range and, thus, outside of their range. Hover just outside of their reach, so that if they try and approach you have tons of ways to answer, while still applying pressure and being ready to strike if there's an opening. A lot of Marth's moveset is nearly unpunishable so long as you keep yourself spaced. Nair autocancels out of a shorthop fastfall, dtilt has insane IASA frames, a spaced fair against a shield applies pressure and isn't really punishable because most of Marth's moves will come out and hit first before anything else can reach you (and most stuff can't reach you anyway), etc. You should, theoretically, NEVER get shieldgrabbed as Marth.
As for Falco, I think the most important and easiest thing to work on right now is just tech skill. Don't miss l-cancels, don't accidentally use fair when you jump out of shine instead of something useful, learn how to sweetspot all his recovery moves from a lot of different positions, etc. That sorta stuff alone will allow you to increase so many of your options and improve a ton of your game. Good thing is, none of it is that hard if you practice and practice with the right mindset. Practicing tech skill mindlessly is BAD, you just train sloppy muscle memory that ends up letting you down once you're in a match. When you mess up in practice, look at it, think about it, and realize how you messed up and how to fix it. Learn how your hands work with the controller, because everyone likes controlling the game a bit different. Find shortcuts for things that look hard (i.e., runoff to shine-upb edgehog looks like it might be technical, but when you realize all you have to do is runoff, do a half-circle from down to up towards the stage, hit the b button at down and the b button at up, it becomes silly how easy it is).
I imagine you probably know a lot of this already, but you don't play like it. That's the most important thing. Don't just know what to do, train your instincts and hands to naturally do it so it actually comes out during a match. Getting better when you practice against people requires conscious effort and analysis to rid yourself of bad habits and start playing like you know you should.
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