When you're ribbing, remember that when you turn your work, the stitches change appearance. Even though you knit a stitch on the first row, that now is a purl as it faces you. That's what you need to look at. Whatever you did on the previous row is done. You only address the row you're looking at.
So as you do ribbing, you knit the knit stitches (the v's) as they face you and purl the purls as they face you.
Also, if your last stitch is a purl on a row and you turn it, you start with a knit, or vice versa.
If you are having trouble purling, it sounds like you may be twisting your knit stitches in the previous row--making them tight. Make sure your needle goes into the front of the loop from left to right--the 'leg' of the stitch closest to you.
This connects to what I said about the stitches as they face you. If you are having trouble purling into the purl stitch that's facing you, it's because the knit stitch from the row before is tight.
I hope all this makes sense.