Two practical notes for when you start.
Trace, do not cut the original. Trace onto paper and grade on the copy. You will want to try the same pattern again with adjustments, and once you have cut the tissue that option is gone. This is also what makes grading low-risk, you can be wrong and start again.
Check the seam lengths after grading. The commonest error is a front and back side seam that no longer match, because the curve was drawn differently on each. Measure both from armhole to hem and adjust before cutting fabric.
Grade the facings and waistbands too. Everybody forgets these, then discovers the waistband is two sizes smaller than the skirt it has to go on.
And one thing that will save you a lot of time once you have done it twice: write your grading down. Bust size, waist size, hip size, and where you blended. It will be nearly the same on every pattern, because it is a fact about you rather than about the pattern. After two or three you stop working it out and start applying it.
The shoulders-first principle in the first answer is the thing to carry into every pattern from now on. Almost every fitting problem people describe as being between sizes is actually a garment sized for the wrong part of the body.