When a pattern says to end with a WS, then you knit the WS row last before you follow the next instruction.
One way to double check is to see what stitch they call for in the next row. If it says to knit the next row, then you know you should have finished up by purling the previous row.
I find this helpful when a pattern says 'end with ws (or rs) facing.' That can be confusing, because, well, I'm sure you can see why.
I check the next set of directions to see where I should be.