During fixed-gear single-engine training decades ago, the plane was
equipped with a "gear" switch with red and green lights. My instructor
recognized the problem of transitioning from fixed to retractable gear
and taught gear operation from day one. Even flying a stinkpot Cessna
172 these days I find myself reaching for the gear switch!

Also, mnemonics are useful, but can also be problematic. For my glider
training I was taught "USTALL", which unfortunately doesn't prompt you
to drop water ballast. Guess who's landed full of water a few times!

My revised mnemonic is "BUSTALL", which is especially appropriate to
those who don't use it and land gear up!

Mike