The following is a tuorital on how to sew an inside pocket into a purse. I learned this technique on Craftster, but I can't find the post to give credit where credit is due. If anyone runs across it, please let me know where you found it.
Step 1: Cut two pockets. I like to use a contrasting fabric from the lining of the purse.
Step 2: Cut two pieces of iron-on interfacing the approximate size of the pocket. Iron the interfacing onto the wrong side of both pocket sides.
Step 3: Mark the middle of your pocket with a pencil. Mark 1/2 inch from the side of the pocket, and 1/2 inch from the top and draw a line. Draw another line parallel to the first line, approximately 1/4 inch below it. Now draw a line inbetween these two lines, all the way across and stopping approximately 1/4 inch from the end. Connect the corners to the end of the center line with a pencil mark.
Step 4: Mark the center of one side of your purse lining with a straight pin. Pin one pocket side to the purse lining (right sides together), 1/2 inch down from the top, lining up your center marks of the lining and the pocket.
Step 5: Stitch along the outside pencil line, all the way around. I use the largest stitch on my machine (5 setting) and find that the distance between the top and bottom line is approximately two stitches. So, I don't try to sew on the line exactly....I just take two stitches and then turn and sew back across. The photo below depicts my sewing around the outside marks.
Step 6: Your next step is to cut down the center line until you reach the diagonal marks. The easiest way to start is to fold the piece in half and make a small snip on the line with your scissors. You can then insert the tip of your scissors to finish cutting on the line. You then cut each diagonal mark to the corner of your sewing.
Step 7: Lift up the pocket and press the seams, all the way around the stitching you just made.
Step 8: Now, this may sound confusing but it will make sense as you work it. Push all sides of the one-sided pocket through the slit until it is on the other side of the purse piece. Press flat.
Step 9: Pin the second pocket piece to the piece that is attached to the purse, and sew completely around the outside edges at approximately 1/4 inch seem allowance.
Now, turn it over and Ta Da!! You now have a nicely finished inside pocket for your purse. You can now attach the other lining piece to this piece and sew it into your purse.