Specificity in Gender
There are some rules which can help you determine the gender of the noun and it will be useful knowing them.
Nouns which are masculine in gender are:
names of men (Lucius), nations, rivers (Tiberis, Sequana), winds (aquilo), months (Aprilis)
Feminine in gender are:
names of women (Cornelia), lands (Aegyptus, Gallia), islands (Delus), cities (Ephesus, Athenae), trees (malus - apple)
Additional notes:
Whereas the trees are feminine, the fruits are neutral in gender. So if you're referring to an apple tree, you'd say malus, and it would be feminine, but if you're referring to just an apple, it would be malum and neutral in gender.
Whereas most cities are feminine in gender, some are not such as Praeneste (neutral). Same is with some lands.
There are also rivers which are feminine in gender: Allia, Matrona (river Marne), Lethe, Styx
I hope this list is helpful. Sometimes it can help you determine the gender. It's very good to know the difference in between the gender of trees and their fruits, for example, as there are no exceptions there. It also doesn't hurt if you know the general gender the islands, rivers and cities follow, as most of the Latin texts mention them.