The #1 problem is watering, either overwatering or underwatering.
Usually it's the former. Next in line is over fertilizing. People
literally kill their plants with kindness.

When people ask me for advice on getting something they *can't* easily
kill I tell them to buy a succulent. They're pretty, low maintenance
as far as not having to prune, don't need much fertilizer, can
tolerate sun or open shade and, most of all only need to be watered
once every week or every other week and a missed watering is no big
deal. :-)

Layne