If you still don't feel well, stay at home tomorrow.
If I don't feel OK tomorrow, I won't come into work.
If you go out, lock the door.
If I go out, I'll call you.
If you have a problem, call me.
If you see Tom, tell him to call me.
If I see Keith, I'll ask him to call you.
If you get there before me, wait in the lobby.
If I get there before you, I'll wait in the lobby.