First off, decide if what you need is more width (room across the front-bust, solved by vertical bust-darts, added stitches made by increases at the bust-points) -or- more length (room down the front-bust, solved by horizontal bust-darts, added rows made with short-rows) -or- BOTH! Depending on the design, construction, yarn elasticity, fabric stretch, and amount of ease, what's required may be different every time.
Vertical bust-darts (VBD) are probably already familiar to you, because they're just like waist-shaping only positioned at each bust-point instead of at the side-seam. Horizontal bust-darts (HBD) are usually the ones that trip people up. Do you knit socks? Basically, HBD shaping is just one-half of a big wide short-row heel.