Do you knit continental style, or do you knit completely the opposite of regular "English" style knitting? Some lefties find they cannot knit in a conventional fashion, even while holding the yarn in their left hand; it requires special control of the right hand needle which dominant lefties do not have.
Personally I am left-handed, but I knit right-handed English and crochet left-handed, but my friend knits left-handed English. The only thing I can really say is that you would want to reverse the directions of any instructions that you find, or find lefty-specific instructions (difficult to find as many categorize continental style knitting as "lefty" style). Once you get the basics down it should be fairly straightforward regardling how to continue.