I have two scales I use to measure if a day is a good one.
The first scale is the "Best day/Worst day scale."
For this scale, I first needed to identify my best day(s) ever. The best days of my life were the days my daughters were born and the day my girlfriend agreed to be my wife. Other things may have happened those days but to me, they were amazingly wonderful. I would not give those days back for anything else.
I also needed to identify my worst day ever for this scale to have a bottom. One hopes that this is harder to do than finding a best day. My worst day was the day my little sister died. It was sudden and tragic and I hope it remains the worst day of my life; that no day is any worse.
Once I established my range using those days, I could examine today and see where it lands.
The chances are that today falls right around the middle. Some days are better or worse than average but overall, in my world, that counts as a good day.
The second scale I use it the "Percent of the day" scale.
For this scale, I needed to break my day into tasks or events. For me, I have the broad categories of "sleeping", "going to work", "working", "time with family", "eating" and "other free-time stuff". That all makes up 100% of my day; 24 hours.
For me to have a bad day, it needs to be more that 50% bad. That means that I have to have more than 12 hours of bad. So many bad hours rarely happen in one day. Most hours for me are, at worst, only OK but many (if not most) are good hours.
What's more, when you start breaking your day into basic components and are mindful of the parts that are making them less-than-good, you have the awareness to know what has to change.
Part of making today a good day is knowing what makes it so and that scale will have to be specific to your needs. Find your scale; and step on it.