One of the most important considerations would be to know the correct size of underwear to purchase. If you have no idea what size your partner is, the best strategy would be to search in her closet the next time she is out of the house. The size would be written on the label in letters and numbers. Make sure you check on a few different items, so as there is no confusion when you hit the stores. The wrong size would not be appreciated at all, and in fact may end up having the opposite effect to what you desire.
If you are not living together, finding out what size to buy may not be so easy. In such a situation, you may need to request assistance from one of your partner's friends or relatives. But only ask for help from an individual you know you can trust completely.
Once you are clear on the size, the next consideration would be to choose the right kind of fabric. Perhaps you already have an inkling as to what type of material she usually prefers. If so, your task will be made easier. Be aware that woman's lingerie from Fatal Woman comes in a range of different materials. If the piece is not to be worn everyday, there is the option of choosing a special material such as silk.
It would likely be a big mistake if you were to go for a design that is in some way outrageous. This may have the result that your wife or girlfriend feels cheap and dirty. Try and understand what type of models she would normally wear.
It can be worth requesting help from the assistants in the store that you visit. You can describe your partner so that they have an idea of what kind of woman she is.
