The Millennium is the promised 1,000 years of peace, where wickedness will vanish and Christ will reign upon the Earth.
The Earth returns to Garden of Eden conditions and guns, for one thing, won't exist for long in the Millennium!
Scripture/doctrinal searching and extrapolating, here are some probable changes I suggest MAY COME in life and the earth during that 10 century period:
--Farming will be the universal trade. Families will ONLY eat what they grow (Isaiah 65:18-23), but then with Garden of Eden conditions (no weeds, perfect weather), that shouldn't be a problem, as everyone will be green thumbed!
But this also means that there may be no urban areas anymore. People will live on small farms or have gardens very nearby.
Sprinklers and irrigation may cease to exist. Weeding and fertilizers will not exist either. There will be no deserts (D&C 133:29).
--Temple work will be the other predominant profession. Only those still mortal can do temple work, but resurrected beings will return to provide exact family ancestries. Errors in past temple work will be corrected. Adjustments in the eternal marriages of some will undoubtedly be done.
--Pornography, risqué paintings, movies, videos and the like will all be destroyed. (Every corruptible thing will be consumed, D&C 101:24). How much of your video/book collection will survive? The Las Vegas Strip will likely go up in flames, but there will be new scripture to read from the Lost 10 Tribes. Weapons of war will be made into tools (Micah 4:3).
--Meat eating will not exist. Fast food will be gone. Animals, like lions and tigers, will presumably become vegetarians and will lay down with sheep in peace. Isaiah 11:7 states that the lion shall eat straw, like the ox. There is some sort of physical change here, where everything from bears to man will no longer need or have a desire to be carnivorous. Hunting will no longer be a sport or allowed and guns will be unnecessary. What purpose lions, tigers and the like will have then is unknown .. Will they become large pets? Cows can give milk; sheep wool, but snakes? Death will be in the twinkling of an eye, followed by a resurrection of likely all people and animals.
--There will be no disease. People will live to 100 years old and then die and be resurrected in the twinkling of an eye (Isaiah 65:20, D&C 101:29-31). No CDC will be needed. No immunizations will be needed and the common cold will be "cured."
--Boat travel may no be necessary. All land will be brought together to one single mass, even islands cease to stand alone. (D&C 133:23). The City of Enoch will return and may rest in the Gulf of Mexico, if you believe some theories.
--There may not be any mountains or valleys (Isaiah 40:14, Doctrines of Salvation 2:316). That means skiing or snowboarding or snow may cease to exist. There may just be a continual summer season, no winter or fall for sure.
--The skies will change. The very earth, or maybe solar system, will move nearer the Kolob realm, thus changing most constellations in the sky. But you may not see stars anyway, because it may be light 24 hours a day (Zechariah 14:6-7).
--Professions that will likely cease to exist: butchers, cattle ranchers; zookeepers; fishermen; gunsmiths; policemen; soldier; attorney; reporter (at least investigative); dentist; many doctors; psychologist; loan officer, lobbyists, spy, king/queen/dictator; mortician; grave digger; salesman; weatherman, English or Spanish teacher; plumber.
--The government will be a theocracy, with Christ as the head. No more democracy.
--Animals may be able to communicate with man. After all, the serpent spoke in the Garden of Eden.
--People will really rest on the Sabbath.
--There will be no Aaronic Priesthood. (D&C 13).
--There will initially be those of other, non-LDS faiths on the earth, though all must accept the truth by the Millennium's end (History of the Church 5:212).
--There will only be one language spoken — the Adam Language (Zeph 3:9). Perhaps the veil will be lifted enough for everyone's original language to return.
--A continual resurrection will take place, where those in the spirit world who accept the truth and are worthy are brought forth. (D&C 88:99).
--Prayers will be answered quickly (D&C 101:27).
--I'm unclear on transportation and what will exist. There's no way polluting gasoline-powered vehicles will remain, but what?
--How many homes, buildings will there? With security and perfect climate and no darkness, some may be unnecessary. (There were apparently no structures in the Garden of Eden!) Will there be bathrooms? The usual bodily waste may not be part of a terrestrial body. Fat and baldness may vanish as well.
-They will likely be NO alcohol, as the decay and fermenting processes that exist now will have vanished forever.
-There will probably be no different races. All will be white. (2 Nephi 5:21).