Mold in showers grows due to the damp environment and humid environment that bathrooms have.
So to prevent mold from growing in your shower you should install a vent fan in your bathroom to help extract the moisture in the bathroom.
You should also use a dehumidifier and wash the shower down and then wipe the shower down often using some vinegar or bleach to help kill any potential mold spores in the shower.
I use a dehumidifier in my bathroom and have a vent fan installed in the ceiling that I turn on when I'm taking a shower and then I also wipe the shower down using some bleach and then dry the shower off.
I haven't gotten anymore mold growth in the shower since I've done that stuff.
You can use bleach or vinegar to kill mold in the shower and then spray it on the mold and let it sit for 10 to 20 minutes then use scrub brush to scrub the mold out of the shower.
Then run the shower to wash the mold down the drain.