I teach a fitting class and this is what I think is crucial.
First of all, Fit as you sew. Do not just sew up a garment entirely and wish for the best as many sewing students do.
You should be fitting at least 3 times minimum while there is still time to make adjustments. The shoulder area tends to be a problem area (usually too long) and can be easily remedied by trimming. Sleeve will still fit in, if not to drastic of a change.
Try a garment right side out first to get an idea of how things are fitting. Then turn the garment inside out and start marking with pins where you need to make changes while you are wearing it. This makes it easier for you.