The reason there's this post is solely because we've seen many times that fighting game beginners were taught in a wrong way or wrong things. And that causes a great pain in our heart.
What we have here are super secret advices (read: what most people fail to tell you actually) for people who are starting a fighting game or tempted to play one.
1. You won't play like a top player in the first 3 years. This's very true for a popular 2D fighting game that has a lot of characters. The time you need to invest in a fighting game is proportional to the competition and the number of characters.
2. Button-mashing is the fastest way to get you killed. Contrary to what some people say, it's not how fast you can push buttons in a short period of time (unlike CPM in Starcraft). In a fighting game, pushing a button will bind you to an animation making you unable to do something else and vulnerable to an attack. If it's Light Attack button, you'll probably be fine since it has shortest animation. If it's Strong Attack button, you'll likely to get punished if your attack doesn't connect. Strong attacks and special moves have long animations, you don't randomly use them. You do it when you think it WILL connect.
3. It's useless practicing combos. Know first what's the point of comboing. In a competitive match, both players don't have many chances to land their attacks. If they do, they must do as much damage as possible, by chaining or linking one move to another. But why bother with comboing when you can hardly land an attack or don't know how to approach. On top of that, a combo comes by itself when you're ready for it. You'll slowly learn to add an attack after the first one. Once you start a short combo, it will eventually become longer and longer as you play.
4. Check the damage output. Some people who don't understand fighting games think that you're supposed to do more complicated things. The truth is you could play decently by using mostly normal moves. Some special moves and combos are harder to do but only do slightly more damage or even less damage than normal moves. Go to the training mode and check the damage output of all your moves, then, while you're at it, all moves in the game.
5. Know all characters. This's the hardest thing but also the most valuable thing. You must first at least learn the properties of every moves in the game, to avoid getting capitalized. What's the range? Where's the blind spot? Can it be blocked? Block standing or block crouching? Is it a throw/grab? Is it a projectile? Is it triggered by your action? Can it be nullified? These are the properties of a move. Games that have more characters need more time to learn because of this. The advance step, the thing that separates top players from average players, is knowing what's punishable by what and best punished by what and having the skill to execute it.