Cook her favorite meal... if possible leave work/school a couple hours early to prepare everything so it can all be ready by the time she gets home from work/school so it's more of a suprise... use lots of candles.. afterwards run a hot bubble bath for her, and if you're lucky she might let you join ^_^

Just make sure whatever you do, for that night - the attention is all about her. Don't talk about what Billy found underneath his porch today. It's all about her.