The fact that you are here and asking how to get better already puts you above many other players, so congrats on that.
I do recommend that you read up on the stuff that others have posted and watch videos to absorb as much information as you can.
Now what i DONT recommend is playing other fighting games (online). Not yet anyway. Playing fighting games in general will teach you a lot about how they work, there is no question about that. However i believe the biggest barrier to people entering fighting games are people getting frustrated and quitting because they get burned out. While older games are perfectly fine to play, the playerbase for these games has been sieved away and the only players who are left are people who will be able to stomp new players with relative ease. A lot of people will get frustrated losing 30+ games in a row without a single win. An experienced player should be able to shake it off though and move on, but it can be a crushing ordeal for a new player to experience that and be left wondering if fighting games are truly for them. Learning how to handle losses is a big part of fighting games though so just be prepared for it.
This is also why it’s important to play a fighting game close to it’s release as this is when you get the best chance of playing people around your skill level. It all sounds a bit doom and gloom and im not saying to abandon the older games altogether. At the very least you can try em out, go in training mode to practice your movement and how the game handles and even try out against the CPU, but just be aware of the situation if you do decide to play other people online and if it does get frustrating, just know that you’ll probably have a better experience once SF5 drops. It would be better if you can find a local scene to hook up with, that way you can explain that you are a new player looking to join the community. Most communities should relish the chance of new blood coming in and should try to ease your way into fighting games.
Most of all just try to have fun with it, you will eventually get better over time the more you play, and as you start to understand more how fighting games work.