Keep your partner's preferences in mind
Since the gift is about your partner and not you, you need to keep his./her preferences in mind. If you are in a new relationship, you can either ask your partner directly about his/her likes and dislikes or talk to to his/her friends and family for suggestions.
Don't copy what others do
Just because a cousin or friend of yours is doing something doesn't mean you should do it as well. While there is no harm in getting inspiration from others, you should try to come up with an idea which isn't very common.
Don't repeat themes
You should try to work on new themes and not repeat old ones. For instance, if you gave you partner a heart shaped gift box with a heart shaped chocolate box and a necklace with a heart last year, you should try to get different stuff this year.
Choose his/her favorite colors
Incorporating colors your partner likes is also important when putting together a themed gift set. For instance, if you know your partner to be crazy about black, use black as a base for your themed gift set.
Organize everything neatly
Even if you have a box of chocolates, flowers, a music CD, a lovely handkerchief, a purse, a mug and a necklace, you need to organize all this properly in a gift basket to get the final impression right. Giving all these things separately will mellow down the effect of these gifts and it won't be as surprising for your partner.