It's difficult to find a good pair of jeans. Don't throw that almost-perfect pair into the back of your wardrobe just yet. If it's the waist that is causing your problem, all you need to do is alter it to tighten that part. While you could take it to a seamstress to have it adjusted, you can do the same thing on your own at less than half the price. Alterations in the waist and hip area of the jeans are called darts. These are triangular tucks that are tapered on one end and wide on the other. Darts should be wide enough at the waistband and are designed to take up the extra inches on the waist. They taper downward to the hips and end at a portion where your trousers fit you perfectly.
Put the trousers on inside out. This will allow you to take more accurate measurements because you'll be able to mark the actual portions you need to work on.
Next, take two pinches of fabric from the waistband. Adjust the tightness of the waistband and mark the pinches using your safety pins.
Mark the part on the hips where your jeans fit perfectly. This point may differ at the back and the front of the trousers so you want to measure both portions and mark from at least 7.5 cm (3 inches) from the centre seam (back) or the fly (front). This is where your darts are supposed to end.
Remove your jeans and take measurements of the portion that the pinches took up and include the area where the pins are. The total width in both pinches will be the amount of material you have to take from your waistband.
You want to get the extra material from the centre of the front and back sides because the side seams of your jeans usually have rivets that can make it difficult for you to sew from the top of the pockets.
Using your tailor's chalk, mark the area where you're going to place the darts inside the jeans. Draw a straight line in the middle of where your dart is supposed to be. From the centre line, measure half the amount you need to take from each dart and draw sloping lines down to the point where your trousers fit properly (the part of the hips that you marked with another pin).
Fold the triangles in half (using the centre line as guide) and pin them in place. After that, sew your darts in, and you're done.