Since the 1st person and 3rd person singular have the same conjugation endings, context and subject pronouns will indicate the subject if it is ambiguous. Look at the examples:
(Yo) jugaba al fútbol los domingos (I used to play football on Sundays.)
Mi hermano jugaba siempre al tenis. (My brother always played tennis.)
(Yo) tenía un gato. (I used to have a cat.)
Mi vecino tenía un conejo. (My neighbor used to have a rabbit.)