The Provisional Cast on

I find the best method for a provisional cast on is to use a crochet hook and waste yarn.  The waste yarn should be a smooth, non-textured yarn of the same weight but contrasting color as your main yarn. 

Using a crochet needle (one size larger than your knitting needle), chain as many stitches as you need cast on adding about 5 more chain stitches.  After you have the chain, knit into the "bumps" of the chain stitch.
When using this provisional cast on it is important to work the first row with the same stitch, either a knit row or a purl row.  If you work a row where the yarn has to be thrown from front to back, it will make the "unzipping" of the provisional cast on almost impossible.

Happy Knitting!