SSBMTutorials, my dude. TONS of information on most characters and techskill. Once you have decided on a main, STICK TO THIS MAIN. It better be a fun main though, if not then melee will become boring. Then go to SSBMTutorials, on YouTube, and watch all the videos on your main. If you can't decide, they also have a series of introducing characters to newcomers, you should give it a watch and see which character suits you.
Also, check out the melee library, posted above, TONS of information, more than SSBMTuts.
I recommend either choosing Capt. Falcon, Marth, or Sheik, as these three are easy (cough sheik) and teach you the fundamentals of melee. You should prioritze Short Hopping and Fastfalling. These techs are vital, and they give you more control over your character, and in a game like melee, movement is essential. Once this is done, you will want to learn L-Cancelling, the single tech that is responsible for melee's fast paced metagame. MASTER L-CANCELLING, and then move on to Dash Dancing, a tech that is useful, and easy, in the neutral. Then learn wavedashing and wavelanding, which expands your movement options. Next learn Shield Grabbing, Shield Dropping, and waveshielding, essential techs to use in defensive play. These are arguable to the most basic and useful techs in melee, and you should learn them ALL. PRACTICE MAKES PERFECT. Spend 30 minutes each day practicing these. After this you may move on to more situational techs, all of which are listed in Wak's Advanced Guide, found in the Melee Library.
Finally, play A LOT and FREQUENTLY. Preferably against a friend, or on netplay, as humans play differently than CPUs. This is how you will form your playstyle and neutral, so its vital to begin this early on. Don't get discourage if you lose, because Melee is HARD, it's takes on average 2 years to git gud at this game, so please, be patient.