That's a quite simple, regular rule. Only the end of the adjective will change.

For example: adjectives fast, slow, tall, small, good, colourful.

rodzaj męski [male (singular)] ends with y/i - szybki, wolny, wysoki, mały, dobry, kolorowy

r. żeński [female (singular)] ends with a - szybka. wolna, wysoka, mała, dobra, kolorowa

r. nijaki [neutral (singular)] ends with e/ie - szybkie, wolne, wysokie, małe, dobre, kolorowe

r. męskoosobowy [male (plural)] ends with y/i - szybcy, wolni, wysocy, mali, dobrzy, kolorowi

r. niemęskoosobowy [not-male (plural)] - as neutral (singular)

We use male(plural) if there are at least one male in described group.

I don't know, if my reply is clear and will be helpful, but maybe someone will read and it will help him to remember.