Thought this summary from Helge Kare Fauskanger was well written and worth sharing.
"For starters, imagine a distinctly insular form of Protestant Fundamentalism minus the Trinity (God and Jesus are held to be separate beings, and the Holy Spirit is God's active power rather than a person). Note: Since the Witnesses want to think of their faith as something absolutely unique, they themselves will not agree that they are either Protestant or Fundamentalist.
* Very important to call God by his proper name of Jehovah, and as noted, you must not get him mixed up with Jesus. Jesus is not part of the godhead but "actually" the first created being, through whom Jehovah created the rest of the universe. Otherwise pretty standard understanding of Jesus' role (literal virgin birth, sacrificial death, resurrection etc.)
* The Witnesses are Jehovah's visible organization (the angels are the invisible one). The concept of this supposedly unique organization, and how everyone owes it absolute obedience, is hugely important. The Governing Body of the Witnesses is nothing less than God's channel of information for our age, Jehovah's "faithful and discreet slave". The Bible is revered as God's Inspired Word, but never imagine that you can gain a proper understanding of it except by accepting the wise guidance of the Organization.
* The year 1914 is huge. Its exact significance has changed over the years, but today, the Witnesses will tell you that 1914 was the beginning of the Endtimes, when God (of course invisibly) established his Kingdom in heaven, Jesus receiving kingly powers from Jehovah.
* The End is supposed to come within one generation after 1914. With the passing of the years, this doctrine has become problematic, with various solutions being attempted since the mid-nineties. Currently, the Governing Body teaches that this "generation" is actually two overlapping generations: some who knew those who saw the start of the Endtimes in 1914 will live to see the End. No doubt about it ... but do stay tuned for further doctrinal developments.
* The conviction that we are deep into the Endtimes thus permeates the entire religion, and adherents have spent 100+ years warning the world (or if you like, crying wolf). Any day now, everyone outside the faith will be summarily wiped out by an angry deity in the global holocaust of Armageddon. There is some uncertainty as to how Jehovah will deal with small children, the mentally disabled etc., but at least if you are a sane adult, your future is very bleak unless you become a Witness before the ever-imminent Armageddon strikes.
* After Armageddon, the obedient survivors will be ruled by God's heavenly Kingdom and will spend a thousand years turning the entire planet into a global Garden of Eden. During this time, most people who died before Armageddon will be resurrected into the emerging earthly paradise, and may gain eternal life if (and only if) they submit to the Kingdom.
* Those who die in Armageddon are however excluded and will never be resurrected. So if you don't plan to become a Witness, pray that you will die really soon, before Armageddon strikes and you are wiped out forever. (One might think that the last generation that generally had time to die off before Armageddon will not be very impressed by Jehovah's supposed "justice" when they are resurrected and learn that their children are gone forever for no other reason that of all generations, they were so singularly unlucky as to be the ones that were alive when Armageddon struck. However, Watchtower literature never discusses this.)
* Getting to live forever in the coming earthly paradise, in perfect health and perpetual youth, is the only salvation available to the average believer. Most of the saved do not go to heaven; this is the special privilege of no more than 144,000 people, who are resurrected as spirit creatures instead of resuming lives as earthly humans. The 144,000 select ones will serve as co-regents of Jesus in the heavenly Kingdom.
* The unsaved are simply destroyed; there is no hell, and indeed no immaterial human souls that could go to hell anyway. (Doctrine similar to Seventh-Day Adventism in this regard.) The dead are unconscious and non-existent, except insofar as God remembers them and will eventually resurrect many of them.
* Morals: generally Puritan, with the added detail that having blood transfusions (or just as bad: eating/drinking blood) is totally wrong. Dress modestly (and if you are a woman, don't try to wear pants in Kingdom Hall). No tobacco. Alcohol (if any) only in moderation. Women must submit to their "husbandly heads". Sex strictly within marriage. Gay marriage -- you've got to be kidding. Abortion is obviously completely off the table. Incidentally, it seems aborted fetuses will be resurrected in the earthly paradise. Their murderous mothers, not necessarily.
* Entertainment must be "wholesome". There is a great fear of "spiritism", so anything even remotely touching on magic, ghosts etc. is to be shunned as unclean and dangerous. The entire modern fantasy genre would seem to be off limits. One relatively recent "educational" Watchtower cartoon intended for children shows how a little boy has received a cute-looking action-figure of "Sparlock the Wizard" from a non-Witness friend. His mother promptly guilts him into throwing the wretched plastic wizard away, since wizards use magic and magic "makes Jehovah sad". And we don't want to make Jehovah sad, do we?
* As regards "secular" scholarship and science, Higher Criticism of the Bible goes out of the window, as does evolution. The Witnesses are however Old Earth creationists rather than Young Earth. The universe and the planet may be billions of years old for all they care, but the human race is only six thousand years old, descended from a literal Adam and a literal Eve that were directly created by Jehovah in the year 4026 BCE with no link to the animal world: Sorry, Darwin, you and generations of scientists after you have got it all wrong. Literal global deluge in 2370 BCE. If geologists can't find any trace of it, it is their problem.
* Competing forms of Christianity aren't recognized as genuinely Christian at all, but are referred to as "Christendom", a word that has overwhelmingly negative connotations in Watchtower literature. Three cardinal mistakes of "Christendom" are often listed as the belief in an immortal/immaterial soul, the belief in hellfire/eternal torture, and the concept of the Trinity.
I think that covers the main points.