If you want to get good at Melee, the best way is certainly to play Melee. If you have a computer that can run it on dolphin, I'd recommend downloading 20XX and just start playing around. Watch videos of high level Melee, play around with the different (preferably high tier) characters, and figure out which character you really want to dive into. Once you've picked your character, you want to start with basic tech: wavedashing, dash dancing, SHFFLing, and teching consistently when appropriate. There are guides on youtube that can help you with all of this. Kevin Toy (aka PewPewU) has a lot of great tech tutorials that are mainly geared towards Marth, but really translate to most characters. There's another channel called SSBM Tutorials that has a ton of tutorial videos on fundamentals and character specific techniques. Watch high level players that play your character and pay attention to how they set up for combos and how they chain one move into the next to give you ideas of what you should be looking for in a real game. And if you're playing on dolphin, you should look into netplay, which will allow you to play online with other players (albeit, with a bit of input lag). And once you have the basics down, start looking around for your closest local scene and try to attend some events! Most people in the community are super friendly and willing to help those who are looking to improve. Good luck, man!