I had a love one pass away too last year. On his birthday, I decorated the house with flowers, bought him a card, got some cake, lit candle near his picture on my altar and sang "happy birthday" for him. And in the evening, the entire family went out for a seafood dinner (his favourite), just like we used to when he was alive.
Word of advice: As difficult as it may be, try not to cry or feel sad on that day. Because when you feel sad, your deceased loved ones feel sad and you want to make them happy on their birthday