1 Spending quality time with each other. Be present with each other.
2 Acts of service ie doing things for each other and support each other.
3 Physical touch ie hugging, kissing or holding hands.
4 Word of affirmation ie telling each other that you appreciate each other, and praising each other instead of being critical of each other.
5 Gift giving
We have all of the above preferences but some preferences are more predominant than others. This depends on our personality and partly due to our upbringing and past experiences. I find that if you have a practical personality, you will tend to put more emphasis on "act of service". If you are very proud or were raised up in a hypercritical environment, you might have a preference for words of affirmation. If you are very "feeling" based, then quality time might be more your preference. This has been my observation. I would love to see some research to prove or disprove my observation.