The majority of words that end in -o are masculine.
Explanation
Practice identifying the gender and changing nouns into their plural form.
Words that end in "-ión" are feminine.
Words that end in "-dad" are feminine.
The majority of words ending in "-aje" are masculine.
The majority of words that end in "-a" are feminine (although there are exceptions).
Words that end in "-tad" are feminine.
Words that end in "-or" are masculine.
The months in Spanish are masculine. For example, "El abril pasado me casé."
If the word ends in "-z", the "-z" changes to "-c" in the plural form.