(this post originates here)
Some brands sell sample boxes with different fragrances, inviting you to layer them as you like, others are intentionally developed so that all scents layer well with the others (Nobile 1942, Jo Malone, Lush, Il Profvmo and others). Although in theory it would be possible to mix three or four scents together, this seems stuff for "Little Chemists", on which I wouldn't venture so lightly. Better to start layering only a couple at a time.
Before you begin, you should keep in mind some general rules: woods and resins layer well with each other and with flowers, especially rose, iris and violet, giving them structure; musk scents get along with citrus -whose life they stretch- rose and white flowers; spices are ok with flowers and woods, which share both warmth and crispness (be careful: ginger and coriander are cold spices, so better with citrus fruits!); vanilla plays well with everything (flowers, citrus, woods, and of course orientals), green notes go best with flowers; citrus layer with almost everything, especially flowers and woods. Aromatics and ozonic/marine instead are risky layers... please test before.
Another tip: layering doesn't necessarily mean overlapping perfumes, playing with the position is perhaps more intriguing. To do so, look what happens if you spray perfume one above another or a few cm far: the notes will behave differently because in one case they will mix, in the other way the scents proceed on their paths, and the general feeling will contain both fragrances the way they are. Try spraying one perfume on your wrists and a few drops of another perfume behind the ears, or enter into a scent cloud and then put an edt just behind the ears. Or perfuming the cuffs of the shirt, or a scarf, with a perfume, and your wrists with a different one.
You can play with textures, too: cologne, edt, edp, extract. Excellent results are obtained by applying a body cream or lotion and then spraying a different scented water on the body, or maybe edt only on the wrists. Or, spray edt or scented water on the body, and put two drops of extract behind the ears.
You can also space sprays a few minutes: a perfume will be expressing its top while the other maybe will be entering the heart.
Whatever layer you choose, I would try the result on paper or on a tissue before spraying on the skin, but I already know that the bravest won't do it... in any case, before you meet your girls/boyfriend do some testing, to make sure the result will not kill her/him.
In any case, the point is: have fun exploring your creativity and remember that once you bought a scent, it becomes yours and yours only, and you can do whatever you like with it!