ok, when you're talking about 'using dashdancing' that's both more and less complicated than what you mean.
the simple side is that you mean to position yourself to not get hit - or to create and opening, depending if you're aggro or campy
the complicated side is that basically this is all a mixup. SSBM Tutorials just released a video that less specifically covers what I'm about to cover.
Ok. So ultimately there are two perspectives on winning a match. A good player will alternate between, or blend, these approaches. I'll leave it up to you on how to mix them but I'll explain them both and how they eventually require each other.
Essentially if you're aggressive you want to run up and hit your opponent.
If every time you approach you simply dash forward and grab, usmash, nair, drillshine, sheild... it doesn't matter... it's all punishable. If your opponent knows that you're coming in on the same timing over and over, they'll get a read on what you will do once you get there. They only have to hit you, shield, spotdodge, dash back, so on.
Logically a lot of new players come to the conclusion that sometimes they should camp - however this is actually not an approach mixup.
You and your friend look guilty of this to me.
Try running up to your opponent, and right when you're almost in range of their longest range threat (falco/fox would be dash shffl nair/dair, marth would be rising fair/dtilt/fsmash, so on) wave dash down.
If youve been just running up and attacking over and over you'll see that they might go for a read on your movement but you mixed it up! So react to their failed read and punish by launching into a combo (dont just usmash - combos actually get more percent and feel more fun than just a smash attack. In most match ups a grab is best)
Some people have so much fun with this feeling they never actually approach. They always run up and then don't attack.
Then what the enemy can do is just go hit you while you're wavedashing back.
So then you know that you have to both run right up and attack, and run right up and don't get hit. This is the way to maintain an aggressive playstyle. If you retreat too far - you won't be able to get your punishes and your opponent won't feel pressured.
You have to walk the fine line between being so aggressive you're frothing at the mouth and being so careful that your enemy is never scared and can think clearly against you.
Remember fox is really fast. If you play right people should feel overwhelmed. Most characters don't have any way to deal with his speed and power.
A campy playstyle works just like what I said but you're on the other end. Use lasers to make them feel like they have to approach, then either wait for them to run up and hit you, or run up and hit them before they get to you. (Ive won tournament sets doing very little else, including a three stock comeback from the first time I ever used the strategy)
The psychology of it is daunting especially for characters without a projectile.
Be careful not to give up too much stage to laser. The stage is your best friend. The stage is what keeps you alive- if it weren't for the stage, you'd be falling to that bottom blast line.
Your mixups can have reads too, you might be doing run up attack, run up wait, run up attack, run up wait, and they're predicting you - or you may be platform camping or laser camping in a way that's getting you hit. If you switch from a campy style to an aggressive style, they'll have to compile a new list of reads against you. That may just save your life.
I hope this is enough. The subject is kind of complicated. You'll have to find out a lot more on your own.