Decide on your glove design. How high will it go up your arm? Is it fitted the whole way up, or does it flare out near the top?
Any cuffs or other ornamentation involved?
With your fingers spread out, make a tracing of your hand and arm onto paper or - ideally - medical exam table paper.
Make a note on this tracing about where your elbow is, if the sleeves are longer than elbow length - it’ll be a good point of reference when proceeding.
When tracing, keep your pen perpendicular to the sheet of paper, using the widest areas of your arm/ hand as the outer guide.
That is, while you COULD tilt your pen to follow your arm closer to the point where it rests on the paper, you really want to use the outermost curve of your arm as the tracing guide.
At the top opening of your pattern (furthest point from the fingers), make any adjustments you need to.
I like to measure around my arm at this point as well as around the elbow, and adjust the pattern to be about ½ of those measurements, at those points on the pattern. Just freehand it - spandex is very forgiving!
If your pattern is to flare out at the top, adjust your pattern to be ½ of the desired final opening measurement, at the point of the opening on the pattern.