When you by your knit fabric....give it a tug crosswise to see that it stretches enough as per the guide on the pattern envelope. This will also tell you if the edges will curl when cut/washed. If it curls too much.... do not buy it.
Sewing with knits is really not much different than sewing woven fabric. Use the proper ball-point needle is possible, use a narrow zigzag for most seams, double stitch the crotch seam. The bonus is that most knits don't need seams finished - but you can if you wish for neatness sake. The special stitch that peaceandjoy suggests also works well for sewing seams. If your machine will take a double needle, hems will be a snap too - Google it!
I sewed t-shirts for my husband for work from fabrics I bought by the pound - white cotton knit. They lasted for years. Some I even replaced the neckline ribbing because the main fabric was still in good shape.