A simple rule of thumb suffices most of the time, and native speakers will still understand you when you get it wrong.
But yeah, I wish Spanish omitted genders most of the time like Japanese does. It complicates things and adds very little in exchange.
The real kick in the gonads is verb conjugations. Nearly every common verb is irregular and there are something like 18 tenses, times six subjects. Even many native speakers struggle to get them right.
