The best way to kill a great outfit is to have panty lines. Even worse, is when you try some hot new brand of underwear that claims not to show lines, spend the money, and then realise that you can still see panty lines. Whether you can sew or not, there are cheap and easy ways to create your own brand of underwear that will not show panty lines, and you won't have to resort to wearing a thong or going commando.
Find a pair of light-coloured underwear that you either already own or buy a cheap pair. Not only do you want these to be light coloured, but thin material works best as well, such as a light cotton, silk or nylon.
Ensure that the underwear fits you properly. The panties should completely cover your buttocks from top to bottom and side to side. The elastic at the top should not cut into your skin or your side, but rest comfortably at or just below your waist.
Cut out the elastic from around the legs of the underwear. Even up the area where you removed the elastic by trimming any ragged edges of fabric.
Cut out the elastic around the waistband if the panties are not bikini fit. This eliminates the lines around the waist. If the underwear is bikini style, loosen the elastic so that it will not create lines by cutting perpendicular slits on the lower half of the waistband elastic. Space these slits out and only cut half way through the elastic. This loosens the waistband and you will not have a line.
Try on your new no-show panties and make adjustments wherever needed. Make sure the legs are comfortable and that you cut out all of the stitching so nothing rubs. Double-check the waistband. Loosen it by pulling and stretching it out by hand.
Use a pair of your underwear as a guide to make a pair of underwear out of a T-shirt in your size. The soft T-shirt material is comfortable for no-line panties.
Trace the front and back panels of your underwear onto the shirt. Cut these out and sew together on the sides and in the crotch.
Sew a thin layer of elastic around the waist to keep the underwear up.
Don't get picky about even lines as you will not be able to see the edges when you are done. Just make sure the underwear is comfortable.