Expect omicron to hit hard and fast; much faster than delta which was much faster than early in the pandemic.
If you are vaccinated and boosted, omicron will be hard to avoid but hopefully not terrible for you as an individual: the vaccines should, with a bit of luck, mean this is more like a flu than something you go to the hospital for. With a bit more luck, you won't get long-haul. I am still considering traveling.
The danger is more collective: delta brought down hospital systems in some countries, and brought America's hospitals to the edge. Omicron is likely to be worse, suddenly.
That's our very short summary. An excellent longer introduction is The Atlantic's America Is Not Ready for Omicron. If you want to see the scientific understanding as it unfolds, check out Your Local Epidemiologist's December 13 Omicron Update, or check her blog for newer information.
What do you do as a traveler?
I think omicron isn't going to stop me from traveling. I don't want to spread Covid. My priorities:
(1) A plan if I get sick. Odds of catching Covid while on the go are pretty high. I plan to ask hotels what they do if someone gets sick. Outside the US, a hotel willing to make very simple accommodations like coordinating restaurant deliveries to your room. And certainly a hotel that won't kick you out of your room if you have to stay a bit longer because you are sick. And of course — be bit careful, wear an N95 not a cotton mask, wear my mask on the bus even if no one else is. It's not middle school, follow the science and not peer pressure.
(2) Avoid places with collapsing hospitals. As a healthy vaccinated traveler, we do need to watch out for hospital collapse. America's hospital system is already battered: health care professionals are already exhausted, have put themselves and their families through entirely too much keeping conspiracy-theories alive. Wherever you are going, check the condition of the hospitals. Watch out for exponential growth in cases in the week before you go.
As of mid-December, in the US, omicron looks likely to hit the East Coast before the West. For myself, just guessing, I might hope that vaccinated tropical countries are hit a bit slower than winter. Costa Rica looks great, right now: very low case rate, their vaccination rate surpassing that in the US
See Where to Travel Right Now (not yet written)