TBH I don't think there's a hard and fast rule about what shots to play or not to play.
Its more about learning to adapt to the situation: to the bowler, the pitch, the field, to which shots you're struggling with this season and which you're middling every time. With time you develop a kind of instinct as to which shot is going to get you out, and learn to put that one away in the locker until next week. You look at how the ball is coming off the pitch or whatever and you get a kind of premonition about how you might get out; nicking one to slip or spooning one to mid off or playing over one that stays low, or whatever.
Furthermore, I don't think this only applies to opening, and I don't think it only applies to early in your innings. If the pitch is occasionally staying low, it doesn't matter if you're on 10 or 60, if you try to pull a back of a length ball like you would in nets, eventually you will get hit on the knee in front of middle.