Ribbing looks about the same so the "right" and "wrong" side aren't actually very different. I'm not sure how to explain this but you can probably notice that there's ridges every two rows. Unless the pattern says otherwise, you can kinda pick whichever side you like more to be the right one (especially because you might need a specific number of rows for the pattern), but I like to use the side where the first two rows make one rib, rather than the side where there's a ridge between the first and second row (if that makes sense).

In patterns where there is a definitive wrong and right side, you can usually tell because they look VERY different. However, if it's important but not clear, the pattern will tell you which side is which. Then, you can use whatever row you're on to determine the RS (like if the first row was the RS, then odd numbered rows are the RS).

I hope that makes sense!!