How to Love Your Gryffindor:They're idealists. It really is the thought that counts. Make the big gesture. Send flowers to them at work. Write them a poem. Volunteer at their favorite cause. Make them dinner. Sing them a love song, even if - especially if - you suck, at singing, because then your Love is overriding what Everyone Else Says. Do something romantic in public. Go overboard. Tell them they're the kind of love that you read about in storybooks. Tell them they're special. Make them feel Romanced.
How to Love Your Hufflepuff:It's all about the togetherness, the commitment, being in the same groove. Spend time with them, even if it's inconvenient. Cuddles and back rubs. Stay in bed together an extra twenty minutes on your day off. Get to know their friends/family. Become at least familiar with their fandoms. Make something together. Try something new together. Tell them your life would be gutted without them in it. Tell them they're beautiful when they're in sloppy clothes. Take care of them. Make them feel accepted.
How to Love Your Ravenclaw:They want it concrete. Do a chore for them that they hate. Let them know you deleted your ex off Facebook for them. Memorize their favorite things and important dates. Keep souveniers. Ask them what they want, don't assume. If they are enthusiastic about a subject, make at least an effort to learn about it. Communicate, communicate, communicate. Ravenclaws panic if they have to guess what you're feeling/thinking. Show them they matter, don't just tell them.
How to Love Your Slytherin:They want to feel important. Get them something frivolous or a little luxury, even if just whipped cream on their coffee. Send them to a spa for a day, or set up a makeshift one in your room. Leave them little coupons they can redeem for kisses/hugs/time/sex when they want or need it. Ask them what they need. Don't ever attack them for spending too much time on their clothes/appearance. Ask them about themselves. Give them "me time." Pamper them.