Courtesy of the Teacher’s Manual to Latin by the Natural Method, I learned a mnemonic for remembering the gender of many of the Latin nouns in 1st, 2nd, 4th, and 5th declensions. (3rd has many of each gender, so those are a different story!)
I have made a PDF of the “Hand Rule” to illustrate this useful memory aid. Each finger represents one of the five declensions of nouns–see the illustration below and the PDF for the summary of gender(s) found in each declension. I hope it helps you keep track of your Latin noun genders even better!