Seneca, Moral Letters, 101.7b-8a: "The one who puts the finishing touches on their life each day is never short of time."
Live each day as if it were your last is a cliche used often. According to stoicism, you have control over today more than yesterday. Yesterday has already happened and you have no way to change what you have already done. But today is the day that you can change and do it.
You also have control over the future, so, today think about what you want to do today or in the future and start making a list. Obviously most of these items on the list will have to be done in the future, but once you have this list, you need to daily start working on them, not in the future. Ask that girl out on a date, go buy that car you've wanted, or seek that ultimate job that you want, TODAY.
I know this is easier said than done, so lets just start with something simple like choosing a lifestyle change (type of food you want to eat, etc), and as you do more little decisions like this, it will be harder to live each day as if it was your last and continually make changes that you want TODAY.