The best way to practice would be to netplay/wifi/local fights with someone else.
But, a good way to learn alone would be fighting lvl 9 cpus that you find really hard to deal with (personally, i think level 9 cpu peach is a MONSTER!). Also use other characters to fight against lvl 9 ike, this way you learn the strong/weak points of the character you are using and Ike!
I hope I helped you, Good luck!
honestly I wouldn't recommend lvl 9s because cpu ai is pretty weird in this game. If I do cpus I play against lvl 3 or lowers or I'll be in training mode and I'll be playing to practice tech or comboes. Most of my practice comes from playing someone else. If you do face someone else always try new things, see what works and what doesn't. Take mental notes of what your opponent does when you do something, and try to figure out if its a habit or a reaction and adapt from there. Hope I helped and didn't just tell you something you already know haha.