When you get this sort of instruction, it means that it doesn't matter if you're off a stitch or so, just as long as you make the required number of increased stitches.
How I do it: If it's only a few stitches like 5-6, I divide the row to make the increases on in half. Then I divide the number of stitches in half (if odd, then the odd stitch increase will be directly on the division place of the row) and space them approximately (say, 1/3, then 1/3, then 1/3 again) before the half-way mark. And repeat the thirds on the second half of the increase row.
Not a precision-type of operation. Approximates work just fine.