Get the lead runner
The runner closest to home is the dangerous one. When you have time, go get THEM.
The rule: If the runner in front has to run and you have time, throw to the base ahead of them.
Which out?
Not all outs are the same.
Runners on first and second. If you throw to first, you get the batter — but the runner from second is now on third, one step from scoring.
Better
Get the runner closest to home.
Step on third instead. The runner from second is out, and nobody is near home plate. The batter reaching first is the least scary runner on the field.
Bonus
And the force is still on.
The batter standing on first still HAS to run on the next ground ball. You kept the easy out for the next play, too.
Only if you have time
You need two things: a force, and time.
A clean, normal ground ball gives you time. A slow roller or a ball that knocks you over might not. If you're not sure you can beat them there — the next lesson is for you.
You make the call.
Runners on first and second, nobody out. Hard grounder to you at third. Where is the play?