A key command from God in the bible that is preached incorrectly almost 100% of the time is the proper following of the Sabbath (for the purposes of this article, I am exclusively referring to the minor Sabbaths; not the high Sabbaths). In almost all of the Christian churches, this is said to be on Sunday. In almost all Jewish churches, this is said to be on Saturday. Well, guess what, their are both wrong. Whether the discrepancy is intentional or not, we can only speculate. However, the bible gives quite clear guidance when it comes to the Sabbath.
There are Sabbath days outlined in the bible: the new moon and the 7th day (again, not discussing the High Sabbaths here). The new moon is just what it sounds like; a Sabbath on the new moon. The new month marks the beginning of a new month in biblical time-keeping. Please note however, the new moon has been slightly distorted in modern times to mean no moon. The new moon discussed in the bible refers to the first visible crescent over Jerusalem. This one gets a little tricky for those of us not living in the holy land. Luckily, most of the time it is the same across most of the world. On top of that, there are many online moon-phase sites that allow you to look up the phase of the moon anywhere in the world. Just be aware: typically the moon is not visible until it is 1-2% full. This means that if the site you are looking at says that the moon is .5% full, that day is not your Sabbath.
"Thus saith the LORD GOD; The gate of the inner court that looketh toward the east shall be shut the six working days; but on the sabbath it shall be opened, and in the day of the NEW MOON it shall be opened. And the prince shall enter by way of the porch of that gate without, and shall stand by the post of the gate, and the priests shall prepare his burnt offering and his peace offerings., and he shall worship at the threshold of the gate: then he shall go forth; but the gate shall not be shut until the evening. Likewise the people of the land shall WORSHIP at the door of this gate before the LORD in the SABBATHS and IN THE NEW MOONS" (Ezekiel 46:1-3).
"...as the new heavens and the new earth, which I will make, shall remain before me, saith the LORD, so shall your seed and your name remain. And it shall come to pass, that FROM ONE NEW MOON TO ANOTHER, and from one Sabbath to another, SHALL ALL FLESH COME TO WORSHIP BEFORE ME, SAITH THE LORD" (Isaiah 66:23-24).
"And God said, “Let there be lights in the expanse of the heavens to separate the day from the night. And let them be for signs and for seasons, and for days and years, and let them be lights in the expanse of the heavens to give light upon the earth.” And it was so. And God made the two great lights—the greater light to rule the day and the lesser light to rule the night—and the stars." (Genesis 1:14-16)
"Therefore let no one pass judgment on you in questions of food and drink, or with regard to a festival or a new moon or a Sabbath." (Col 2:16)
The second Sabbath is the 7th day of the week. This is for a number of reasons. One is that 7 is a holy number (a discussion for a different article). Another is that 7 represents the day God 'rested'. I put rested in quotes because it is somewhat of a mis-translation in the bible. God does not rest. He never tires. It was more of a day of reflection and appreciation of his creations. The seventh day is to be counted from the first of the month. Remember, in the bible, a month starts on the new moon. So, to outline how this all plays out:
"Six days shalt thou labour, and do all thy work: But the seventh day is the sabbath of the LORD thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates: For in six days the LORD made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the LORD blessed the sabbath day, and hallowed it." (Exodus 20:9-11)
"Six days thou shalt do thy work, and on the seventh day thou shalt rest: that thine ox and thine ass may rest, and the son of thy handmaid, and the stranger, may be refreshed." (Exodus 23:12).
"Six days may work be done; but in the seventh is the sabbath of rest, holy to the LORD... " (Exodus 31:15).
"Six days thou shalt work, but on the seventh day thou shalt rest: in earing time and in harvest thou shalt rest." (Exodus 34:21).
"Six days shall work be done, but on the seventh day there shall be to you an holy day, a sabbath of rest to the LORD..." (Exodus 35:2).
"Six days shall work be done: but the seventh day is the sabbath of rest, an holy convocation; ye shall do no work therein: it is the sabbath of the LORD in all your dwellings." (Leviticus 23:3).
"Six days thou shalt labour, and do all thy work: But the seventh day is the sabbath of the LORD thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, nor thy manservant, nor thy maidservant, nor thine ox, nor thine ass, nor any of thy cattle, nor thy stranger that is within thy gates; that thy manservant and thy maidservant may rest as well as thou." (Deuteronomy 5:13-14).
You have a Sabbath on the first sighting of the new moon over Jerusalem. Then, seven days later, you have another. Seven days after that you have another. This continues until you come to another new moon. So, the first of the month, eighth of the month, fifteenth of the month, twenty second of the month, and the twenty ninth of the month are all Sabbaths. While, technically, the lunar cycle only has 28 days, the new moon is not visible on the evening of the 28th. This means that the next day is still a seventh day Sabbath. On that 29th day, you can usually see the new moon. Therefor, the next day becomes the new moon Sabbath, and will also mark the day of the week for the next 4 Sabbaths. This means that once a month you will have a week with two Sabbaths. Typically, they are back-to-back, but I have found that every once in a while there is a day in between due to the percentage of the moon that is illuminated.
One more very important note that you may have already picked up on: the biblical 'day' starts at sundown. It is explained this way in the bible, but also comes about because of the moon being crucial for the calendar. So, the 'day' according to the bible runs from sundown to sundown. Which, quite frankly, makes alot more sense than starting the day at an arbitrary point in the middle of the night (aka midnight).
I fully understand that, for most people, this is not an easy commandment to follow. Modern society has made sure of that. My advice is ask God for forgiveness on this one, and do what is in your power to remedy it. Maybe, as we end up working more and more from home, you will gain more flexibility with your schedule. Maybe you can make extra time for prayer on the Sabbath, and make an active attempt to keep God in your thought throughout the day. Maybe you make a special meal/feast. Maybe you even have an understanding boss, who will work with you on this one. No matter how little it is, do what you can do. I am sure God will notice the effort. Plus, don't be shy to ask God for help on this one. I usually don't advocate for much self-centered prayer, but this really isn't for you is it?