I can't go in depth now, but mostly you have to be extremely quick, and always moving. Because we are outranged, we need to abuse our speed to the max. Fox also has safe aerials that he can use in the neutral to set up combos, or just beat out certain attacks. Learning how to walk effectively is a MUST imo, because you can be way more precise with your spacing adjustments by walking, and using the tilt stick, you can throw out a quick Ftilt the opposite direction if they whiff. Fox's walk is better than almost every walk in the game. You can approach opponents, but never approach with dash attack (should be reserved as a punishing, combing move in most situations). Before you approach, you have to figure out what the opponent does when you rush them. If they like to shield, you can use a safe AC bair, do a dash grab, or crossup with Dair, nair, or bair. If the opponent likes to empty hop and bait a lot, use your lasers to get them moving. Just be careful not to get too greedy with your shooting. Against slow opponents, lasers are AMAZING, so abuse them as much as you can. Overall, learning how the opponent plays is the most important thing, because fox has so many options that he can use in certain situations. Before you get a grasp for how the opponent plays, play it safe, watch their habits, and look for openings for punishes. If you play it right, you should be able to gather enough information to fight the opponent based on their tendencies. Always watch to see if they change their habits, and adapt accordingly. That's all I have for now, but I could write so much more on this subject. When I have the time, I may make a doozy of a post about it, but that's for another day.