To connect a fsmash, you can chaingrab characters (most notably Sheik) up to around 80%, then fsmash in the direction of their DI. Also, it works to interrupt some shield grabbers if they try to grab when you are spaced too well. If you get an fair shielded, for example, just l-cancel into an fsmash. They should attempt a grab, but you will lean back and hit them right in the chest with a flaming purple elbow. Works way too often :D.
Don't attempt it too many times consecutively though, because they may catch on and just shield the fsmash too...leading to a succesful grab.
To connect a Dsmash: this usually only works on roll behinds. If an opponent is shielding near the edge of the stage, simply whiffing a few fairs with jabs will pressure them to roll behind you, where you can just turn around and catch them with both kicks of your dsmash. You can also not turn around and just hit with your back kick, and it will launch them closer to the edge of the stage, and this can easily lead into an fair, or uair if you aren't daring enough.