I was commenting on Sheila's post below and thought I should share this tip with everyone. Tink is knit spelled backwards and it is the safest, slowest and most frustrating way to unknit your mistakes; one stitch at a time. However, you have to do it that way if you are working lace and some cable patterns. But for stockinette and garter stitch mistakes you can usually rip out your mistakes by the row.
A little ripping out trick I use, take your yarn needle and a contrasting yarn and go back to your last "good" row of knitting. Run the needle and yarn through the stiches of that row. Either run it through the first leg of the stitch or the second leg of the stitch - but be consistent.
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After all of your good stitches are picked up let it rip; pull out all of the bad stitches. When you get back to the good row, place the stitches back on your needles and remove the contrasting yarn. Take a deep breath and knit on.
I have done a lot tinking and ripping, if anyone has any tips on tinking please let me know.