All of C.Falcon's smash attacks are pretty situational so these are the ways I use them:
You are not gonna hit someone with The People's Elbow very often, but when you do, you know it's gonna do big damage. The best ways I get free fsmashes are from locks. The easiest lock set up is dash-fthrow -> dair or pivot ftilt on the missed tech. If you do that, you have a free, partially charged fsmash and you'll end up getting almost 40% from the start of the match. The set up isn't guaranteed though.
Other than that, the only way I land fsmash is from HARD BOILED READS. Against a recovering opponent, just hold down A at the ledge to condition them to do a ledge roll, then turn around and slam them with the godly elbow.
Some people don't know that you can actually do an fsmash directly from a dash by waiting for the end of the dash and fsmashing the other direction. It's easiest to do while foxtrotting and using A to smash. This makes fsmash really versatile so it makes it easier to land one while reading landings or rolls.
Down Smash is awesome to use almost anytime to use while near someone because of its decent speed, range, power, and doesn't have a lot of lag for a smash attack. The best place to use it is on someone against the ledge. They can roll away, so they either take the hit from the front, block or spot dodge the hit from the front, or roll and get hit. It aplies a good bit of pressure here but it's pretty good to use anywhere IMO.
I don't use up smash too much, but it can be useful after fthrow at low percents or at the ledge. I know it's probably better than we think though.
Just some ideas on some situations in which to use these. They work pretty well for me, another long time Falcon player, so I'm sure someone with your skill can put these to use.
Falcon be with you