If you are only half sure on a decision, try and gauge the player's reactions. If the GK goes for the ball as if setting up for a goal kick, delay your decision and then point for a goal kick, same with a corner. If there is no reaction, go with the goal kick because it is the "safest" decision. However, if you have given the corner and were unsure, and the player is indeed looking at you like you've pissed on his kids, never change the decision on the player's reaction. Wait for the ball to come into the box and give a "soft" defensive foul. And when I say soft I mean give anything, even if it's outrageously marginal. Refs do it at the top level and it's easier to sell it on a public park. You would rather not have a goal being scored on a decision you think you have messed up. But only do it when it is a complete mess up and never just a debatable decision.