im not very experienced in the matchup either, but since
jigglypuff has
the one of the best edgeguarding/gimping games in Melee, the general rule should be to not go off stage unless you have something secured, such as an edgeguard or a wat to get back on the stage without losing a stock. Also, you should always fight for stage position, meaning that you always want more of the stage behind you than jigglypuff does. And, as you said, "I fell flat because I wasn't spacing right, and I didn't mix up my approach". Spacing is as important to you in this MU as it is for Jiggs. and NEVER go into the wall of pain. it sets up for more bairs or combos involving rest/insane edgeguards. My input. Happy Smashing!