We have now arrived at our theoretical waist in
our theoretical bottom-up, knit in the round pullover. All the
decreases are done, leaving us with 267 stitches at the waist. Here's what to do from there on up:

1. Work even for a bit.
Usually, patterns will tell you to work even at this point for about
an inch. This matches the reality of some of our bodies: Unless we have
other bodacious curvages going on, our torsos do not generally start
getting bigger until just under our rib cages, which is a bit above the
waist.
Extra customization tip: Take a tape measure, wrap it around
your waist, and then, holding the ends together loosely, slide it
upwards until the ends need to expand a bit. How far up from your waist
are you? That's the length you ought to "work even" for yourself,
because that is the vertical distance in which YOU are the same
circumference.
Extra sanity note: Don't sweat this "work even" distance too
much if you are just a beginner. Work even for an inch, and then see if
you like the finished effect. If not, make notes for next time.
2. Measure fullest part of bust.
We're not going to talk about bust shaping just yet (not yet, notice
I said NOT YET!), in order to keep this simple. Taking a tape measure
to my Girls, I notice Mother Nature is doing her usual sometimes up,
sometimes down thing with my bust size, so today's number is a 41".
3. Choose preferred ease at bust.
We'll keep this simple and use the same ease we've used for the rest of the garment: 1.5" positive ease.
4. Add bust measurement to ease to get finished bust measurement of sweater.
41" plus 1.5" equals 42.5" finished bust measurement.
5. Calculate how much you need to INCREASE (we're going up, remember?) from waist (narrowest bit) to bust (wider bit).
Finished bust measurement minus finished waist measurement: 42.5 minus 38 equals 4.5".
6. Determine the number of total stitches to increase, waist to bust.
Take the result from #5 above and multiply by the stitch gauge: 4.5"
times 7 stitches per inch equals 31.5, which we will round up to a nice
even 32 stitches to increase.
7. Measure the vertical distance over which the increases will be worked.
Measure from your waist to the fullest part of your bust and then
subtract 1" (to compensate for the work even section in #1). Waist to
bust length for me is 8", minus 1" equals 7" over which to work the
increases, or 91 rounds (7" times 13 rounds per inch).
8. Work out the spacing of the increases.
We'll do four increases for each increase round, so 32 stitches to
increase divided by 4 equals 8 increase rounds needed. 91 rounds
divided by 8 equals one increase round about every 11 rounds.
Summary: From waist to bust, I will work even for one inch,
then start increasing four stitches each increase round, with one
increase round worked every 11 rounds. Again, I will continue to work
one increase on either side of the "side seam," just for consistency.
And that, my friends, is Waist Shaping 101! We did kind of a
beginning overview, because there's lots more tricks and tips about
where to put the shaping, how to shape using needle size changes and no
decreasing/increasing at all, and much more.

Other posts in the Waist Shaping Series:
Waist Shaping: An Overview
Waist Shaping: Not Just For Waist Anymore
Waist Shaping: The Math, Hem To Hip
Waist Shaping: Choose Your Curves
Waist Shaping: From Hip to Waist
There are no stupid questions, remember...
Next week, I'm going to take some of the questions and comments you
have shared and answer them as best I can! So if there's something
about waist shaping you have not understood, or if you have a burning
questions or comment, post a comment and your question might end up being answered by yours truly in next week's Knitting Daily. —Thanks; I always love hearing from you! Sandi

Sandi Wiseheart is the editor of Knitting Daily.
What's on Sandi's needles? You know how it is. A friend tells
you she's preggers, then invites you over for Easter dinner. Am I the
kind of person who can show up without a tiny handknitted baby gift in
my hands? No. I am not. Thus, I am quickly knitting the most adorable
baby jacket ever.