For example, sometimes I would take a medicament mechanically while doing something else and just a few minutes later, forget if I took it or not. Solution: say loud to myself "I'm taking a pill".
Another: sometimes I'd lend some amount money to a colleague, and a few weeks later I'd have a hard time figuring whether they gave it back, and they too. Solution: I tell them to hit me (or do some other stupid thing) when they give the money back, so we both remember.
Going even further, sometimes I have to set a reminder to myself like "take an umbrella when leaving tomorrow morning because it's gonna be raining". Putting umbrella close to the exit, or doing a phone reminder do not always work, particularly when I'm in a hurry. One thing that works is doing some notable physical disruption in the environment, like putting a can of tomato sauce, upside-down, close to the exit.