Do things that show her that you love her, that you have thought of her, have considered what she likes and does not like.
Do things that demonstrate you "get" her and are willing to follow her love language.
Listen to her.
Tell her or write to her what you appreciate about her, what you would miss if she were not in your life.
Be nice to her.
Consider doing a favor for her.
Consider finishing that project you started. Help around the house without being asked. Get a babysitter for your next date.
Let her influence you on something you both deem important.
Buy her a nice outfit and take her out, showing her off, being proud that she is with you.
Kiss her and rub her back without expecting further intimacy (no strings attached).
But please do not be romantic!