For a neat lower edge, pick up the required stitches from the main piece of knitting. Begin by slipping a small DPN through a straight line of stitches, picking up the left leg of each stitch, in the position required.
Join in the yarn at the right of the stitches (leave a long tail for assembly) and use a correct-size needle to knit the stitches from the small needle.
Using a smaller needle will make it easier to pick up the stitches neatly, without distorting the fabric.
Knit the pocket to the required length, ending with a few rows of ribbing or other edging, as required, and bind off, leaving another long tail. (Choose a cast on that will give a firm edge without pulling the fabric. Avoid stretchy bind offs since these can go baggy over time, giving an untidy finish.)
Use fine, short DPNs to create straight lines for seaming. Pick up one leg of every alternate stitch along the vertical line at each edge of the pocket. Thread a piece of matching yarn onto a bodkin and join the two vertical seams by going through the edge stitch of the pocket and then through the stitch on the DPN, matching the rows. Work to the top of the pocket edge and fasten off.
When going through the loops be careful not to split the yarn for a neat finish.
Repeat for the left edge, working from the top down if this is easier. In this case, you may find it helpful to pin the pocket in place to make sure that it stays aligned with the right side and that the rows match to the main fabric. (A k2, p2 rib has been used to finish the pocket to match the welt and cuffs. Ribs give a snug but elastic top for pockets that bounces back into shape readily, making it suitable for an edge that will get lots of use.)
<b>Working a Straight-Slit Pocket:</b> -Working in stockinette stitch, make a separate pocket lining to the desired size of the finished pocket using the same yarn as for the main fabric. -Knit the main fabric to the row where the pocket opening will be (the top edge of the pocket), finishing on a WS row. -Knit the next row to the location of the pocket. Bind off the same number of stitches as your lining. (If making a pocket edge, don’t bind off but transfer the same number of stitches as used for the lining from the main fabric onto a stitch holder.) -Place the lining stitches onto the LH needle with the RS of the lining facing the WS of the main fabric. -Knit across the lining stitches and continue knitting the main fabric to the end of the row. -Knit across all the stitches as normal (the lining stitches replace the main fabric for the rest of the piece). -On the WS, sew down the lining as above.
This knitting pockets how-to is excerpted with permission from <a href="http://www.amazon.com/gp/product/1438001711/ref=as_li_qf_sp_asin_il_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=1438001711&linkCode=as2&tag=craftfocom-20">"Complete Knitting Skills: With 27 Exclusive Teaching Clips to View Online"</a> by Debbie Tomkies and published by Barron's Educational Series.