You're doing good so far. You just have to know the combos because executing them is easy. Learn to read oppenents attacks and REM. Know what attacks can REM on reaction, like one of Ivy's BE is two hits and the second hit can be REM. Same with Viola. A lot of Viola orbs can be REM. Also Yoshi's CE can be REM, but no good player would whiff a Yoshi CE.
If someone blocks your attacks, you generally wanna stop, unless your feeling ballsy and REM after anything on block. When someone gets out of your 1 or 3A+B, you have the frame advantage (i think) so 6B after if someone gets out of it. Always block after a 33AA even on hit cuz you're like -10 on hit. Don't be a afraid to spam REM also, unless it's someone like Patrokolos.