Women love flowers.If you don't know her favorite buy her a single rose or big bunch of roses.Actually the flowers has subconscious influence over women.Her mind will interpret one rose like: "Baby you are the one for me"; and bunch of flowers like: "He'll make everything for me ".Do this often and every time try to surprise her.Sometimes you can put flowers on different places for example.
Attach a note "You are the one for me".

Spare time for taking her on some beautiful places - mountain, beach, island.Don't go on big hotel or big city.You don't need places with many people.You need to spend a lot of time away of other people.
Take her on sunset. Take her on the place where were your first date.Always tell that you love her, that she is the one and you can't live without her.

Romantic dinner.This will take effect for sure.The dinner have to be like surprise.Include champagne, tasty food, candy, put candle on the table.
You also can take her on dinner on small romantic restaurant.

Women love to be seduced.Always tell her that she is your queen, that she is the most beautiful woman on the world.Kiss her like it was the first time.

Start to kiss her suddenly (when she don't expect that) and say "I love you".

Suddenly start to kiss her - five or even ten times.

Put one rose somewhere.Do this from time to time.Every time change the places and the type of flowers.

Surprise her for her birthday.Decorate one room with flowers, balloons, confetti.

If you want to learn more tips, ideas, advices, I recommend you this book.