The Jasmine Bra (available in my sewing pattern shop, Ohhh Lulu Sews) is a great bra pattern for a first-time lingerie sewist! It is simple to assemble, and will give you experience applying lingerie elastic. It's a comfortable bralette that can accommodate a number of sizes with some simple pattern adjustments. I use this pattern a lot myself. You may remember I made a boned bikini top with it last summer. I'll also show you how to add padding in another Pattern Hack Post.
First we need to know a little something about how cup size works. Cup size is basically the difference between your Bust & Band measurements. For the novice seamstress, your bust measurement is measured around the fullest part of your bust, and your band measurement is measured around your ribcage, just below your breasts where your bra band sits. In general, each Cup Letter represents 1" difference in Bust and Band measurements. So, as an example, if you have a 30" band measruement and a 34" bust measruement, you should fit a 30D bra. This is not a fool proof method, but a guideline for finding a size that fits you best. The person with a 30 band and 34 Bust may well find that a C cup is more comfortable or that they prefer a looser band. Regardless, this is often a good starting point.
I have drafted the Jasmine Bra for about a B/C cup size, which is a very common cup size. If you are below or above that cup size, you will likely want to make some pattern adjustments.
If you are an A or AA cup, you may generally have a 0-2" difference in bust to band measurement. As a result, you will want to straighten out the curve of the cup (See the illustration below in the orange ink). The front princess seam gets taken in at the bust apex, which is approximately 3.5" up from the lower edge of the pattern piece. When reducing the cup, I haven't adjusted the height of the pattern pieces, just straightened out the curve of that front seam.
If you are a D-DD Cup (or larger!), you will want to exaggerate the curve of the cup as well as increase the height to provide better coverage. Here, in purple ink, I've increased the bust curve by 1/2" on each pattern piece at the apex. I've also extended the top of the cup by 1/2".
Because this pattern is to be sewn in stretch knits, the fit is really quite flexible. If you are above a DD (this includes myself!), you may find that this simple adjustment, adding 1" to the bust apex + a bit of height, will be all you need to get a better fit. Remember, it is really important when sewing any garment, but especially lingerie, that you sew a mock up first in a fabric of a similar weight and stretch. This way, you can make any pattern adjustments to get a truly custom fit!