1) The Right Size. Of all the "duh" things to say, right? But though very often I hear people advising to make sure that the stays are not too *small,* less is said about stays being too *big.* If stays aren't fitted properly, they'll actually be far more uncomfortable than if they fit snugly. They won't support, they'll encourage poor posture, and, perhaps worst of all, they'll shift and chafe. Avoid too-loose fit and too-loose lacing for comfortable stays.
2) Mind the Gap. I've seen more than one stay-wearer annoyed that her new stays didn't meet at the center back--that is, she thought they were too small for her because there was a gap at the center back lacing. Not at all! You want a bit of room to shrink, as it were--even if you aren't planning on losing weight. In addition to normal weight fluctuations, I've found my body adjusts a bit to stays and snugger lacing is needed later in they day or on day two of wearing. (Note: This is not waist-training, just my body settling into a different--and probably better--posture). Additionally, stays can stretch a bit over time. Buy yourself some extra space and make yours or have them made with some space to spare.
3) Stays are Unique to You. Remember that differences in extants represent not only differences in style and fashion, but also differences in human bodies and lifestyles. Look at a dozen or so extant pairs of stays. You'll find that you'll be able to point out similarities and differences between each; no two will look exactly alike. Some of those differences are certainly due to changes in fashion over time. Others are due to expectations for what that particular set of stays would be worn for and what they were made of (were they a high-fashion pair for a high-born lady boned with baleen, or a workaday set boned with reed?), based on socio-economic status and other factors. Some differences even emerge as distinctive to the wearer's body shape. Perhaps the bust is narrower or wider in relation to the waist, or the tabs placed differently, or the angles of the panels different.
So many differences, for instance, here--straps vs no straps, more purely conical shape vs a flat front; no tabs vs tabs, fully boned vs partially boned. The list goes on!
Met Museum, c. 1780Wool with reed boning
Met Museum, no date given (I estimate c. 1770-1780), no material given (I guess silk and whalebone)
Victoria and Albert Museum, c. 1770s, silk and whalebone
Very long story short--your body type should be taken into consideration in picking a set of stays or patterning your own. Just as you would in selecting a pair of jeans or a fitted dress. The same things won't work for everyone.
4) Tabs are your friend. Yeah, they're a pain. Even plenty of extants skip them. But I love how tabs ease the distribution of pressure and make the fit so much more comfortable. Bite the bullet, make the stays with tabs. You will curse them while you're binding your stays and love them ever after.
5) Be careful, they're addictive. So I joke about making set after set of stays the past few years, but honestly? They're a very fun project. Limited fabric so they're not an expensive endeavor, plenty of small steps so that you can make some progress with just a couple hours, and so functionally pretty when you finish. Enjoy making a first set of stays, but watch out lest ye be bitten by the staymaking bug!
Any corset-making tips you've gained over the course of your own projects?