Best strategy against Fox:
1. Get him off the stage
2. Edgeguard / gimp
3. Rince/Repeat
lol much easier said than done. Fox is my worst matchup by far. On the stage, he's a beast. Off the stage... well, what can he do? Just edgeguard him, and you're good to go.
Well... what character(s) do you use? We could help you better if we knew what your mains are.
One strategy against Fox (my old strategy) is use Pika, stay close to the edge avoid his attacks and lazers, hope he messes up and backthrow him off the stage. F-Smash kills any chance for a successful recovery. This can backfire, since one hit can lead to a 0-death (or edgeguard situation), and a good Fox will notice your strategy pretty quickly.
Jiggs also works well against pika
I highly disagree. True, Pika is one of the easiest to 0-death as puff, and can be started with many attacks, but a Puff will never hit a good Pika. I just played both sides of the matchup earlier today (although my puff opponent was not the best), and a good Pika with good spacing can avoid getting hit, and abuse priority / range advantage. One mistake by Pika, and it's the loss of a stock, but against a good pika, you won't get lucky 5 times in one match.