I want to be good at this game, but every time I always fail at for glory. I don't know how people know what attacks I do, or how I'm OHKO'd at 40 percent. Can anyone give me advice, or at least fight me and give me advice? (If you want to Skype, go ahead. I'm only 13 though.)
it's probably because your attacks are too predictable. you need to practice more solo before going into for glory. try watching smash videos and replicating some moves, it helps.
It is probably as Isabella said. If you say people are predicting you, it means that you should mix up your strategy more. Another possibility is that the person you played with has practiced strategies against your character and already know how to approach you and deal damage. Playing online imo is the best way to get good. If you find a really good player you can learn what strategies work and what doesn't. Everyone plays different, so the best way to get good is to have multiple strategies against peoples playstyles so you can be ready for anything. However, I would do better at explaining things if I seen how you play.
You didn't mention a character, so I'll say this: stick to one character.
If you're constantly losing, don't switch. Stay as that character and don't make the same mistakes you did last game. This way you'll learn to deal with those bad match ups effectively and have a greater chance of winning. You can also visit other sites and find information on dealing with characters that give you a hard time. I usually go to Smashboards. Here, click this, and click the character you're playing as or having trouble with and look for the thread about match ups. It's usually a sticky. You should also review frame data to see how and when to use a move and how it compares to others.
If they know what attacks you're going to use every time, switch it up. Maybe he launches you and expects you to come down with an aerial so he shields it and grabs you. Instead of doing that next time, try landing without doing anything and grab him for staying in his shield (or use a command grab in the air like Wario's Chomp or Mewtwo's Confusion). Also notice patterns in his playstyle. Maybe he really enjoys going for a spike and always misses or he always rolls back onto the stage from the edge. Predict when he'll use it, airdodge, and punish with a spike of your own or stand in the spot where he'll be rolling to and charge up an up-smash. Also mix up your recoveries. Maybe you always use tethers or always recover low instead of high. Don't use the same one because that's just asking to get gimped or meteored.
Find friends. Playing alone sucks and can get boring and frustrating. If you have a friend also wants to get better, great! You both can practice against each other often and get better together. You can help each other with certain problems by playing as a character until figured out. It's much more fun this way.
Try participating in tournaments both offline and online. You're pretty young, so online might be best. It's completely different from For Glory and you will most likely find some new tricks that you can use on others. It's definitely a great way to see how much you've improved.
Then some playstyle tips: Try to avoid rolling. A lot of players know how to punish people who roll often. Use quick moves to approach. Don't use a move you have to commit to especially on shield. You'll get grabbed and feel silly. Something like Sheik's or Ness' f-air is good for this. Don't use your shield to block attacks all the time. They'll notice this and you'll get grabbed or even end up breaking your shield.
I have a few tips for certain characters from my experience playing as and against Yoshi:
Link - If you're going in the air, never land in front of him. If you must, try doing it without throwing out an aerial and get close enough to use your jab. If you notice that he's grab happy when you land, bait it and punish.
You should only use eggs in the air. Using them on the ground leaves you vulnerable.
Definitely study his patterns. A common one I see is boomerang to arrow and repeat. Bombs are usually pulled out in the air. If he's holding one in the air to recover, bait out an airdodge far away from the stage so that he's out of range and immediately head back to the stage. You'll need your second jump to go back off stage in case his bomb goes off, and if it does go for the spike.
I also recall his smash attacks being able to block arrows and the boomerang. Not sure if this is much help.
Mewtwo - Throw eggs to disrupt Shadow Ball in the air. If he shield's it, use an aerial and land behind him or else he'll get the grab or use Confusion (better than getting grabbed, you can punish it with a n-air easily due to how fast it comes out). If he's still in his shield, don't throw out an aerial and just grab him. Make sure to land far enough away that he can't grab you. You have more range.
Lucario - Similar to Mewtwo, throw eggs to disrupt Aura Sphere, especially in the air. During early percentages, Aura Sphere is pretty weak and you can even block it with a move instead of your shield. It also has a lot of end lag so a grab would be the optimal punish if he misses or you powershield close enough. Space him out as much as you can because he loves to grab, especially Force Palm(technically it is a projectile).
Robin - Your eggs can reach further than Arcfire and Thunder, so use them, especially in the air. Elthunder and Arcthunder are slow so you can shield or dodge(dodge is best because s/he'll run to combo you if Arc lands). When s/he's fully charged, try staying in the air more often. It's much harder to land Thoron and there's quite a bit of lag at the end. Keep track of how many times s/he uses the Levin sword and specials so that you can steal the book/sword or prevent Robin from grabbing it. Not sure if you would count Nosferatu as a projectile, but s/he can't use it off stage whatsoever or s/he will SD.
Most of this is applicable to any character. The only difference is that you have eggs you can throw quickly in the air while others don't have a projectile like that.
More experienced players will be able to counter whatever you do though, in fact, they wouldn't even rely on spamming because good players know how to approach (unless it's a Sheik player... those needles.)