Movement

Before we can discuss strategy or advanced techniques, we need to talk fundamentals. As a Marth player your fundamentals are everything. Mastering the core aspects of the game greatly benefits you, even more so than when playing most other characters. It is absolutely crucial that you be spot on with all of your basics; and among all things that could be considered "fundamental" to Marth, I believe that the two most important are: Movement and Spacing. Spacing is extremely difficult to master, and all but impossible to perfect. Good spacing requires good movement. Getting comfortable moving with Marth will be your first learning goal.

Dashing

Although it's not wise to think that jumping is bad, try to remember that as Marth you are most threatening when grounded. As you may already know, Dash Dancing is the basis for all of your ground movement. It is performed simply by tapping left and right repeatedly on the analog stick while grounded. If your taps are done shortly after each dash and before the maximum dash distance is reached, then the dash animation will be canceled by a dash in the opposite direction. Dash Dancing is maintaining this state of constant dashing. With proper timing you can also chain together multiple dashes in the same direction, which is known as Fox Trotting.

Running

During matches you will be spending much of your time dashing, but running is important too. If you tap, and then hold the analog stick left or right for a long enough period of time you will initiate a run. During your running animation your options are limited to: Shield, Jump, Grab, Running Attack, UpSmash, and Crouch. Crouching during a run will end your running animation, allowing you to use any of your standard grounded options, many of which are not possible during a run. This is known as Run Cancelling. Using a run cancel followed quickly by a Dtilt is something you should practice early.

Jumping

There are different heights of jumps in Melee. If you press jump and release it quickly enough, you will do a Short Hop that is much lower than your full jump height. Marth is a generally "floaty" character, and falls rather slowly in the air. However, you can Fast Fall by tapping down on the analog stick while falling. Keep in mind that if you're trying to fast fall after a jump that you must tap down after the apex of your jump.