It's dreadful, but I constantly find myself using fSmashes, even at lower percents. So I have 2 questions:
How can I learn to not use it at low percents?
and
What are some good alternatives for mid-range percents with less lag?
Play with a bot and use ONLY aerials for a while. I've had that problem playing marth to break that habit so you just have to force yourself to use your all-important aerial and grab game to win.
Good alts can be like approach and run up with
short or full hop nair.(recommend nairs most)
Good old spam
fair to zone and space it.
Down tilts are really safe to use also if you can zone and mix up with fairs and nairs
A
pivot back air would be a nice change (charge enemy and before too close reverse and back air),
Ftilt is good and even better if you can find the tipper on it (lot harder to find than fsmash one),
Hell if enemies shielding you can (short hop option)
Neutral B for shield pressure or for people on low platforms above you.
B forwards if you can time it and enemy doesn't see it coming (has a quick release but a bit of after lag).