Let us start with colors, as you know valentine is identical with soft and cute color such as red and pink. Usually people will match those color with something more neutral such as white or silver and gold.
However, if you want them to be more unique, you can actually use any other color to match it such as purple, blue, green and many other colors you like. Adding this color will actually add more personality to the decoration that you create. But remember to keep it adequate and not using too much color.
Next is to use the common valentine signature for your valentine mantel ideas. This include the heart shape, the cupid and many other characters that is associated with this event. Of course, you do not need to use it too much or you can even skip them all if you want the decoration to appear neutral and not too valentine looking.
When it comes to the items that you can use, there is actually no limit on the types of decoration to use. You can try to match it with the theme that you use throughout the room or just use common things that you use on your mantel.
However, you might want to consider adding beautiful things such as flower to the mantel in this special occasion. Then if you want to make it more personal, you can add picture of your love one which will surely add more love to the valentine mantel ideas that you create. Here are some of the examples.
image source : pinterest.com