I’m not even going to beat around the bush with this one. I won’t even make some lofty statement to try to intrigue you to read the rest of this post. I’ll go ahead and tell you the answer:
Learn her love language.
It’s that simple. 
If you learn your wife’s love language you unlock the key to a mystery centuries of guys wish they could’ve decoded.
If you know about love languages, you’re all set. You can skip the next part and pick back up at the “additional resources” part at the bottom.
If you don’t know about love languages, keep reading.
When I was in seminary, one of my professors introduced me to the idea of love languages. I had no clue what they were much less how to use them. I found it weird we were in a class about student ministry and talking about something that sounded like it would apply to dating. But after he explained love languages, it all made sense.
The 5 Love Languages is a book by Gary Chapman. In it, he describes the five basic ways that people give and receive love. They are as follows (all information taken from Chapman’s website):

Words of Affirmation

This language uses words to affirm other people.

Acts of Service

For these people, actions speak louder than words.

Receiving Gifts

For some people, what makes them feel most loved is to receive a gift.

Quality Time

This language is all about giving the other person your undivided attention.

Physical Touch

To this person, nothing speaks more deeply than appropriate touch.
Most people have a primary language and a secondary language. For my wife, her primary language is quality time. Her secondary language is physical touch. Sitting on the couch together watching a show we DVRd without distractions is one of the best ways I can show her I love her. Sure, I could buy her a gift or say something nice to her, but she wouldn’t respond as well to that as she would to simply spending time together.
Your wife may be different. 
Receiving gifts may be her top language. If so, the gifts don’t have to be extravagant. A simple $2 trinket from the drug store could mean the world to her if it’s thoughtful and unique.
If words of affirmation is your wife’s top language, writing her a note or telling her how you’re proud of her could show her you love her better than giving her jewelry
I could go through each language but you start to get the idea.
Every woman (and guy for that matter) is different. We all give and receive love differently. Our minds speak different love languages. Figuring out what your wife’s language is could be the best present you get her this Valentine’s Day.
To learn your love language and to find out hers, take the assessment here.

Additional Resources