For waist shaping and me having a smaller bust than hip circumference, I do about 5 or 6 decreases an inch apart, knit straight for 1 to 2 inches and then do 2 or 3 increases 2 inches apart. I measure the distance from the hem to under the arms and use my row gauge or try the sweater on to figure where to start the shaping.
I place markers a third of the way in from the sides for the back shaping and a fourth of the way in for the front. I use 2 knit stitches between the left and right leaning stitches on either side of the markers. So I knit to 3 stitches before the marker, SSK by slipping the first st knit-wise and slip second st purl-wise, insert left needle in front and knit both slip stitches through the back loops. Knit 1 stitch, slide marker, knit 1; then knit 2 together for right leaning decrease. I use M1R , K1, am, K1, and M1L for the increases.
I am A-line/pear shaped so I do more decreases than increases. If you have a larger bust you might do more increases just on the front. I carry most my weight in the front so on a cardigan I'm making this month, I knitted the front straight and only did the shaping in the back. When I knitted the Hadley sweater in the knit-a-long here, I did the shaping in the front and back but only on the outside of the markers so I was decreasing half the number of stitches.