Kind of person
First thing you need to note is what kind of person is your loved one. If your partner has humorous personality then you can get a funny type card. In case your partner is serious type then buy a simple to the point card.
Go to the store
After deciding which type of card you are going to buy for your partner, go to a card shop or local grocery store and choose a card from there. You can always go to Hall-marks or any local store in order to get the right card.
Buy the card
Buy a gender appropriate card which is not cheap at the same time. Remember you do not want to buy an expensive card for your partner as what is written in the card matters most. You can get card which are of normal rates along with simple and romantic at the same time. You should also not buy a very cheap card as you want to give your partner something to cherish for her life.
Get an envelope
After buying the perfect card, get an envelope which should be of appropriate size. Remember that envelopes are usually placed behind the cards. In case they are not present, ask the shopkeeper to give an appropriate sized envelope.
Write a note inside the card and make your loved one feel more special. You can write a joke and other stuff as well. However, a simple romantic message will do the job.
In the end, deliver the card to your partner. You can simply give it by hand or mail it if you are not able to meet your loved one on the special day.