Learn from yesterday: Learn from the mistakes you did yesterday so that you do not make them again. Once you learn the lessons of yesterday’s mistakes, forget them; otherwise they will make you fearful of the future. Also do not develop nostalgia for the past- you can savour the past for some time but do not get stuck there- the past is not reality.
Live for today: Today is the only day you can actually live. No actually, you can only live this moment. But for practical purposes, let us call it a day. Live in day-tight compartments, as Dale Carnegie used to say. Yes, you can prepare for the future, but there is no point in fretting and worrying about what the future will bring. So live in the present, live for today.
Hope for tomorrow: The future is not unimportant. Hope for the future. Prepare for it but do not worry about it. Do the things you can control and leave the rest to God. Be optimistic about the future and set goals. Do not be anxious as it does not help you in any way.