You probably don't have good opponents to play against, but if you happen to play one, here are some "advanced" tips:
First off, save your jump when hit off stage unless you know you're coming in too high to get hit (just save it every time). Make sure you never double jump on the stage unless you're at really low percents, cause if you lose it and get hit off stage, that's bad news for you.
Against fox, you need to watch out for a possible shine spike. You have two options: 1. fair fox away, but this is risky cause if the fox player is good, you will still get shine spiked, or 2. go low so it's harder for him to shine spike you. You can still get shine spiked, but if you see fox going for you, up B into him; you'll get to the stage and fox will be forced to use his firefox to get back onto the stage. Punish the greedy fox player!
Against ganondorf, always go as low as possible and use your jump late unless the player sees that coming and edgehogs. Ganon has an annoying uair which destroys marth's recovery. Falcon has one too, but good falcon players will roll to the edge of the stage while holding down Z to light shield. That way, when marth up B's to the stage, he will either get edge hogged or land on the stage. If you land on the stage, then falcon will fall to the edge then hop up to get a free knee on marth during the recovery lag. So how do you stop this? If you come in high enough, just fair falcon so he is pushed further into the stage and can't fall to the edge. Otherwise, you're going to get hit. I know, it sucks, but you can wreck falcon's recovery too.
Against sheik and samus, you're going to want to watch out for them running off the stage and nairing you to destroy your recovery. If you see it coming, go super low, jump and up B to the stage. You may be able to edgehog them back and punish them, or you may get caught in Samus's up B or sheik's up B. Also, against most characters you need to watch out for the bair either from the stage or from the ledge. In many cases you'll need to go low and use that extra jump you saved.
Always sweetspot the ledge. Learn to press L or R while letting go of the control stick to tech in place, particularly against marth or falco or anyone who hits you when you up B to sweet spot. Just do it every time. You have 1/3 of a second, or 20 frames before u get hit to press L/R in order to tech.
Many times you will want to use your second jump to sweetspot the ledge, and I emphasize sweetspot. You need to be careful against marth, fox, and other characters that you don't get hit with a poke or shine or whatever when using your jump. It's very predictable that you're going to want to grab the ledge using your jump, so you'll need to make sure you go low enough to just barely sweetspot the ledge.
There are a lot of mindgames in the "advanced" marth game, as you can see. If you want to be good with marth, or any character for that matter, you need to have lots of patience when off stage.
Hopefully you know about all the ways to get back on stage while on the ledge and how you're vulnerable for getting hit when over 100%... right? I'm in the midst of writing an essay, and only have 2.5 more hours to finish it, so maybe I'll continue this tomorrow.
!(sorry for any grammer errors,spelling errors,wrong words in general, it's late -_-)
