When designers put these two together, the bottom half is predominantly the spotted skirt. Spots are more slimming than stripes and that is why designers do this. In a Westfield Trend Report catalogue I noticed a model wearing a spotted skirt teamed with a white blazer and a striped top. A white blazer was chosen because her skirt had more white than black in it as the spots were small and in an irregular pattern. Her simple top had an equal amount of black & white narrow stripes. The secret is in only seeing a small amount of the stripes so that the combinations are in unequal proportions. With no matching colour in-between, spots and stripes together can look clownish. To keep it modern, add some colour in your accessories. Coloured shoes or coloured bangles work well. To look super-stylish, I would add either matching coloured shoes and bangle and black & white earrings or black & white earrings and bracelet and coloured shoes of your choice. Do not add a necklace as you will lose the effect of the black and white top.
If your spotted skirt has more black than white in it and you have darkish hair, wear black as the middle colour. I once had a black cardigan which has a small amount of black and white stripes at the round neckline. This had the same effect over a dominant black skirt with small white spots as the white blazer and striped top mentioned above.
In the same catalogue was a model wearing a skirt with a diamond pattern which from a distance looked like spots. These graduated the concentration of colour from a more white background at the hem to a more black background near her waist. The skirt had a medium-width black waistband which matched the dominant black colour at her waist. A black belt would do the same job. Her striped top graduated from wider to smaller equal coloured stripes at the neckline. The pleated neckline broke up the stripes into an interesting pattern. She was accessorised with a block colour black & white handbag. This is a harder look to find and pull off. The easiest way to do it is to buy that total outfit or create a picture as your guide.