Ribbing, garter stitch, and seed stitch (and a whole host of other knitted fabrics) are reversible: they look the same on both sides.
But suppose you have to do something (shaping, for example) only when working right-side rows. What do you do if you lose track of whether you’re working a right-side or wrong-side row? How can you tell where you are?
Answer a Different Question First
Where was the cast-on tail when you finished casting on and were about to start the first row?
The cast-on tail can only have been in one of two places: it was either right below where you were about to work the very first stitch, or it was at the far end of the cast-on, below the very last stitch you worked on the first row.
Tail Location of Different Cast-On Methods
Long-tail cast-on has the tail right there below the first stitch you’ll work when you’re done casting on.
Crochet cast-on (my fave and the only one I ever use), cable cast-on, and knitted cast-on all have the tail at the far end when you finish casting on.
If you used any other cast-on, then just think about where the tail was when you were about to work the first row.
Was the first row you worked a right-side row? (Some pattern or project instructions may specify that the first row worked after completing the cast-on is a wrong-side row.)
If the first row was a right-side row, and if the cast-on tail is in the same place now, then you’re about to work a right-side row.
If that first row after casting on was a wrong-side row, then if the tail is at the same place now, then you’re about to work a wrong-side row.
Exception for Long-Tail Cast-On
Some knitters take into account the fact that long-tail casting-on is both casting on and working the first row, so when they start the first row, they might be working either a right-side or a wrong-side row; it just depends. If you’re in this situation, just think it through, comparing the location of the cast-on tail before you worked the first row with its location for the row you’re about to work.
If You’re in the Middle of the Row
All of the above applies even if you had to put the work down in the middle of the row.
Now, where’s the cast-on tail, below the beginning of the current row or the end of the current row? Apply the rules above.
(You may of course have to rip if you’ve worked past the place you ought to have done the thing you were supposed to do.)