Fox is the fastest character in the game, use this to your advantage. He may drop like a brick but he's also built like a brick shithouse. He doesn't fly very much and it takes a lot of percent to actually get him off the edge. Fox can be the best character in the game if you learn to use him right.
You all know the basic moves so I'm not going to tell you what you already know. What I am going to tell you about is how to use the basic moves in different combos to lay an ass kicking on your opponents. What you want to do when an opponent is close to you is shield, grab him, and make sure you do the down throw so when he hits the ground you can use the reflector and add more damage, then when he's about to roll up back kick him twice, then smash kick him forward, this combo is very effective. Also your back kick move is very effective when an opponent is airborne and has a high percent; if you use this move he will fly of almost every time. What makes this back kick effective is that is does adds a high percent, and it is lightning fast. You can back kick and be ready for another opponent in no time.
Your laser can be an effective weapon as well. Although it doesn't do a lot of damage, you can get several shots off repeatedly which will rack up the percentage. The laser is most effective when the game is just beginning and your opponents are trying to decide where to go; for that split second you can get 5-10 shots off effectively. When your shooting someone and they are running at you, be sure to put your laser away quickly because it does take awhile to put it away, and if you take your sweet time then you will get hit. Also this is very handy when you don't know where a mine has landed. All you do is shoot your laser at where you think it could be, and it will hit the mine and the mine will blow up.
I find rolling with fox is only effective when you need a desperate attempt to flee. Fox's speed can usually get you out of a situation that is looking scary. However, if you insist on rolling then rolling comes in handy when a character is about to kick you, just shield, then press over, and you will roll around him, then give him a quick kick so he goes down, then a nice big Power kick. Rolling is also a smart idea to get items due to you giving characters a hard time trying to hit you. In theory rolling is effective but I find Fox's speed alone is sufficient enough to get the dirty deed done (darn cheep).
Now you might think what I just gave you were tactics but those were basic tactics, this is where it gets complicated, not really but it made me sound smart. Now if you want to inflict a lot of damage fast, use your back kick to kick them up, then power kick up to get them further up, then you jump and use your up kick to get them even further, now when all this is being done , your adding about 50% to their health so even if you don't get them off while kicking them in the air, you will definitely put a hinder on their health. Fox's down kick move works like a wet dream when someone is jumping over an edge or a hole in the course. Because all you have to do is jump over them, and your fox its not difficult, and down kick them into the hole. Be careful: though because if you hold down to long, Fox's brick like ways will kick in and he will proceed to fall down the hole. Also when using Fox's jetpack to get back on an edge and a character is standing there not paying any attention to you, just jetpack into him, this will cause him to fly up and you time to get back into your stance to either flee, or fight. Your shoulder check (over and B) is good when characters are at a distance and you can't get them with a powerful enough move, just use this move and you will hit them.
Well I hope I have been of help, because Fox is a really good character, and I find my tactics work, so I hope they work for you as well.