Don't over think it.
Once you can reliably get a good push off, just start trying to do consecutive second deals through the whole deck. Don't worry about the speed, just do the move slowly over and over.
Once you're going through the whole deck without missing any deals, start speeding up to a normal dealing speed.
Once you can second deal through the deck smoothly, start switching it up with legit deals. As in, straight deal to the left, second deal to the right, all the way through the deck.
Once you can do that smoothly, start dealing into positions around a table. Pick one spot to second deal, straight deal the rest of the spots.
The key to a deceptive second deal isn't so much the move itself, it's being able to do it within context so it doesn't seem like something someone should pay attention to - to that end, the best piece of advice I've ever heard for false dealing: Make your seconds look like straight deals, but also make your straight deals look like seconds.
Note - this format works for any false deals and when practicing making all the deals smooth it's a good idea to do all false and straight deals you know in rhythm to make sure they're all smooth and similar. Some people use a metronome for this.