I recommend you not to study the gender of words together with the article and one adjective. It will help you to notice the difference. General rule: la abuela sabia/el abuelo sabio. Exception: el joven inteligente/la joven inteligente ( En este caso, el género está dado solamente por el artículo, no por la terminación del sustantivo o del adjetivo ). Por eso, es mejor aprender así. Si piensas que todas las palabras terminadas en "a" son femeninas, eso no siempre es así. Ejemplo: el papá amable, el pianista formidable. Hay varias palabras terminadas en "a" que pueden usar un artículo femenino o masculino: Ejemplo: El periodista, la periodista/ El publicista, la publicista.

it all depends on the end! Masculine nouns ending in "-o", "-e", "-i" "-u"; "-l", "-n", "-r", "-s". Feminine nouns ending in "-a", "-ma", "-ta", "ion", "cion", "-d", "-z". But do not forget the words of exclusion.

I agree with Rodrigo, So the best you can do is forgetting about genders or rules because you get confused, The best you can do is pick a word and look up in Google images for figure out what gender is. I learnt that by context, this topic is very abstract and difficult if you have a minimum knowledge in Spanish. As a native spanish speaker when I was a child I don´t care about genders because I figured it out by myself, Read as many books as possible, listen as many podcasts as possible, try to get a lot of input of spanish, and then ask for a specific word or group of words. Learn spanish with the "grammar or Rules are the key" is like learn to run before you can crawl. When you read some phrases they have many grammar rules inside them, and you will internalize them easily without thinking about rules.

Well if you dont have an idea you could just start for the easy ones the nouns ending in O are male: Ex: VasO, librO, radiO, colegiO, gatO, espejO, etc. And the nouns ending in A are female, Ex: amigA, maletA, cocinA, casA. First the simple then the rest :) Don't forget that if you use adjetives they have to be in the same gender. Ex: VasO nuevO, espejO suciO, etc CasA blancA, maletA pesadA, etc.

Lamentably you can't know it beforehand, you should memorize when a word is fememnine or masculine,. Equally there are some words that you could recognize if those are masculine or femenine because of the ending ("a/as" or "o/os"). Some of them are nouns and other are adjectives.