How To Prepare Your Fabric
It is essential that you prepare all fabric before cutting it out in order to achieve a better fit and a more professional look. Different fabrics will need different care and the label on the fabric bolt will tell you whether the fabric is washable, dry-cleanable, or if it will shrink. I like to take my pen and notepad into the store so I can write this information down whenever I buy material I'm not familiar with.
The label should tell you whether the fabric has been preshrunk by the manufacturer or if it will shrink, and how much it will shrink.
If the fabric has not yet been preshrunk, and the label says it will shrink more than 1% you should preshrink it before cutting.
To preshrink washable fabric, simply launder and dry in the same manner you would after the garment is finished. To keep the ends of the fabric from fraying simply sew a seam or serge along the ends before laundering and drying.
To preshrink dry-cleanable fabrics use a steam iron and move the iron horizontally or vertically across the grain of the fabric. Do not go over it diagonally because this will distort the fabric. After steaming the fabric allow it to dry on a smooth, flat surface until completely dry. (About 4-6 hours).
Other notions such as zippers and trims may also need preshrinking.
Another thing you want to do is make sure that your fabric is on grain. The first thing you need to do is to straighten the crosswise ends of the fabric. Different fabrics require different methods.
For knit fabrics simply cut along a crosswise rib.
On striped, plaid, or checkered fabric simply cut along a straight crosswise line.
For all other woven fabrics cut into the selvage and gently pull one or two crosswise threads pushing fabric along the threads until you reach the opposite selvage. Then cut the fabric along the pulled thread.
Repeat these methods on both ends of the fabric, then fold the fabric in half lengthwise lining up the ends and selvages. If the fabric is on grain it will lay flat. If it bubbles it is off-grain and you will need to straighten it. All fabrics can be straightened except for permanent-finish fabrics.
To straighten slightly off-grain fabric leave fabric folded lengthwise and pin together the selvages and both ends making sure they line up, then using a steam iron press from the selvage to the fold.
If the fabric is more off-grain and cannot be straightened with an iron, simply pull the fabric in the opposite direction of the slant.
By following the above steps before cutting the material your finished garment will have a more professional look.