Pattern help

I’m just about to start decreasing on the right hand side of a cardigan,I have to decrease to shape for the armhole and also for the front vee neck , is it best to decrease on the purl row ? or the knit row? thanks in advance.

If the pattern doesn’t specify, it’s your choice. You can decrease on either knit or purl sides. Sometimes patterns have you decrease on both.
I prefer to decrease on the public side, the side that will face outward on the finished sweater.