How Do I Practice [Tech]?

A good way to learn execution in Melee involves 3 steps. First is to learn the inputs. Then, practice actually doing the inputs. Finally, get feedback.

Learn the inputs. Look up what the physical button presses are. What inputs give the desired result? Don't forget to think about timing. Execution requires proper button presses and also pressing them at the right time. Think about how the timing can change in certain situations, e.g. L-cancelling with shieldstun vs. without.

Practice the inputs. Start slow. Think slowly and explicitly what the inputs are. "This button, then this, then do that." Try it slowly to start developing muscle memory. Speed up as you become more accustomed to the inputs. Speed up until you start doing the inputs so fast that the inputs no longer give the result. This can come in several forms. One could be that the lag from the first input prevents the second input from happening e.g. you air dodge too quickly and instead of wavedashing you full hop; or you're not in the right place to do the next input, e.g. you air dodge too early when trying to waveland.

This leads into the last point. You need to have feedback to tell when you are messing up your inputs. Have a desired end-goal in mind, and know what it looks like. It needs to be concrete, or at least, mostly concrete. Know what it looks like when you do the wrong inputs. Know what it looks like when you time your inputs too fast or too slow. The frame counter in the 20XX Hack Pack is useful for getting feedback. Do some research to know what the animation of the sequence of inputs looks like. When your feedback tells you that you didn't execute correctly, think about what caused you too mess up. Too fast? Too slow? Wrong button? That's all. Don't tell yourself what you need to do. Your body already knows what it has to do because you looked up the inputs in step 1. Just notice what went wrong. Coupled with the knowledge of the proper inputs, your simple awareness of the feedback is enough for your body to realize how to do better next time. If you need to, take a breath and visualize the desired result. Don't visualize what inputs you have to do (unless maybe you're in the beginning stages, still learning the inputs).