If you're doing a pattern stitch, it's a bit easier, but if it's all st st, then just find the beginning of the CO edge and follow the stitch up. It's a little easier to do if you can stretch the work a little bit between your hands, and you have something in your hand to follow the line with.
If you haven't woven in the tail end yet, can you use that to guide you? I generally knit in the tail end with the working yarn for 3 stitches. So if I need to find the beginning of the round, I find the tail end and count 3 stitches in and follow that column up the rows. If you're following a pattern, find the stitch that is logically the beginning of the new pattern.
Hmm, I found the CO tail (thanks - great idea!) and followed it up, and it made sense. I knitted to what I think is the last st of the round. However, when I compare the stitches, it seems like what I think is that st is higher than the what I think is the first st. But if it truly was the last st, wouldn't it be even with the first st?
The reason the one stitch is higher is because when you knit in the round, you're knitting a spiral and each round lays on top of the other. Think of it like a coil of wire with the end not laying flat.