To create your Civil War reenactment wardrobe, you can't just pick up any calico print from the local chain fabric store. As with every other aspect of your impression, research is the key.
I recommend Juanita Leisch's book Who Wore What, the book Dating Fabrics, a Color Guide, by Eileen Trestain, and The Citizen's Companion, which is a monthly publication dedicated to Civilian reenacting. You can also check your library for books about antique quilts, as these can yield a wealth of samples and information. After all, quilts were made of scraps of garment fabric.
There are also some very good websites you can find referenced here.
If possible, visit some museums to see actual period quilts or clothing.
Types of Fabric
Cotton, linen, woold, and silk were readily available (at least in the North) and most garments were made of some blend of these. A linsey-woolsey or a lawn is next to impossible to find these days, so you will most likely be choosing 100% cotton. Feel free to wear silk, if your impression warrants it. The wool made today is much heavier than the wools of the 19th century. While I hesitate to recommend the use of synthetics, I use and recommend an 80% wool 20% nylon blend which looks and feels like wool, but is much lighter (and less expensive).
You Can't Go Wrong With Solids
The easiest thing to choose is a solid fabric. Pick a cotton broadcloth or poplin in nearly any basic shade, and you will be fine. No lime green or hot pink! A navy, tan, black (for mourning), gray, brown or dusty shades of red, pink, or lavendar would be appropriate. Solids are also usually cheaper than prints, and you won't have to worry about matching up prints and seams. There will be no "wrong side" of the fabric, and you will have less waste. Solids are also a good choice if your impression is that of a less affluent lady. Dresses made of prints and plaids are a sign of wealth, as they require more fabric to make.
Plaids
The plaid family includes stripes, checks, and twills, also. Plaids are woven; that is the pattern of the fabric is created by weaving different colored fibers in different directions. As the war progressed and blockades kept fabric and notions from the South, southern families returned to the arts of spinning and weaving to make their own "homespuns". A small scale check or plaid with a nubby feel would be a great example of a homespun dress. For more ambitious sewers, a large windowpane plaid would make a lovely dress. We might not wear such a bold plaid these days, but it was not uncommon to wear plaid dresses during this period, and it demonstrated the wearer's financial status.
Prints
Prints are the most challenging category. You really have to take several things into consideration. How old are you (in your Civil War impression?). What is your social and financial status? Would you have made this dress yourself or hired a seamstress? Are you a Northern or Southern lady?
And older woman might be wearing a made-over dress from an earlier decade. So you'd look for an 1840's-1850's reproduction print. A young, unmarried woman from and affluent family might have access to the very latest styles and fabrics. Northern women were far more likely to have access to fabrics than southerners, because of the blockades.
Popular Colors for Prints: Indigos, dark pinks, cheddar yellow, rust, many shades of red and brown. Greens were a little wonky back then, but there were plenty of dyes available by the 1850's.
Types of prints: Small scale geometric prints were very popular. These could be used in any direction, allowing for less waste of fabric. The space around the geometric object should be at least as large as the object itself. Skip the calicos. In the 19th century, "calico" was a generic term for any printed cotton, it bears no relation to the small scale florals of today.
Speaking of florals, large scale florals, or florals with birds were used on upholstery, but not in garments. A floral pattern over a stripe might work for a period dress, but most modern florals are just not period correct.
When shopping, look for reproduction designers like Harriet Hargrave, Brackman & Thompson, Judy Rothermel and Nancy Kirk. These ladies base their prints on actual period fabrics.
Don't faint when you see the price tag. $6-$8 per yard seems steep, but your Civil War dresses are an investment. You will sweat in them, get them filthy with camp dust, smoke from the fire, mud from the horses, and goodness knows what from the Port-o-let. The fabric will need to withstand a lot of wear and washing. You don't want it to shrink and ravel up on the first wash!
For a glossary of fabric terms useful to reenactors, click here.