It's always nice to spoil your lady love with lavish gifts, but make sure that your surprise for her doesn't ruin the romantic day.
One such gift which is a no-no is lingerie. Bringing home a size too big will insult her; give her undies she can't squeeze into and you'll depress
Second is a heart mug. Nothing says 'I forgot it was Valentine's Day so I stopped at the gas station on the way home' like a coffee mug.
Also, never give her household appliances or a gym membership.