this guy is obviously new so listing some common gimps for him to try out would be much more helpful than overly general advice.
Here's a really simple gimp/edgeguard against fox/falco:
after you hit them off the edge and force them to use their double jump:
0. force them to use their double jump by edgehogging their attempt to grab the ledge with it. Or just hit them hard enough.
1. jab if they try to side-B to the ledge or right at you. They will be forced to use their up-B.
2. down-B counter their up-B if they wait and use it below the stage, but too far away for you to drop down and fair or up-B. They can avoid the counter by doing a very careful sweetspot from below. If you predict they will go for that, WD to the ledge. Fastfalling will make your edgehog faster.
3. if you react fast enough to them up-Bing below the stage, run off, fastfall a bit below them, then double jump and fair. Up-B and you should be able to make it back. If they are too low to do the rising fair, instead reverse Up-B them. If you have countered their up-B, or jabbed their side-b at a mid-high percentage, you don't have to react. They will always be in a position to be up-B'd or fair'd.