Best way to spend only a day in Rome

Becky, this might be a start?

https://www.ricksteves.com/europe/italy/rome-itinerary

I personally find Rick's 1-day itinerary overly ambitious, and wouldn't do both the Colosseum/Forum/Palatine and Vatican Museums on the same day. The Colosseum and museums are the two most overcrowded attractions in Rome, and the museums can eat up a LOT of time. They're also closed on Sundays so what DAY they'll be in Rome can impact a plan (and what month is their trip?)

To do the Colosseum at 8:30 AM they'd need to pre-purchase a scheduled-entry ticket for that time slot. See "ticket with scheduled entrance time for individuals and for groups" on this website:

https://www.coopculture.it/en/colosseo-e-shop.cfm

They will need to pass through a security-check queue but that's unavoidable. The ticket covers the Palatine/forum as well, and those latter two must be visited at the time time. The Vatican Museums require advance tickets as well to avoid long lines. Anyway, I'd do one or the other but not both, and skip the Vatican unless they have a deep interest in art or the Sistine is a MUST for them.

Since they're staying nearby, there's an interesting excavation (Area Sacra) at Largo Argentina they should peer into. They can view it from the sidewalks above, and there was some signage in English explaining the various buildings when we were there.

http://www.turismoroma.it/cosa-fare/area-sacra-di-largo-argentina?lang=en
http://www.aviewoncities.com/rome/areasacradellargentina.htm

This in their first time in Rome, I gather? With only a day in a city like Rome, I think the key to sightseeing is to simply not go inside anything major. There’s a lot they can see without having to wait (and pay) to see. I would recommend walking the old center, experience Piazza Navona and Campo di Fiori, pop into a few churches (with their amazing art), see Capitoline Hill and the views of the Forum (nice at night), Trevi fountain, Spanish Steps... that’s a FULL day when you throw in a couple nice meal breaks. I’d do a day like that in Rome in a heartbeat.

I would suggest they take an evening walk and see Spanish Steps, Pantheon, Trevi Fountain, Piazza Navona, and other things in the area in the evening. I believe Rick Steves has a "Heart of Rome" walk in the guidebook that covers these areas. They are beautiful at night, and this frees up their day for sightseeing.

I would pick EITHER the Colosseum/Forum OR the Vatican (St. Peters and the museum). Pick one and pre-book tickets so no time is wasted standing in line.
Then after sightseeing the inside of their pick they can go see the OUTSIDE of the other. So if they picked the Vatican, they can see that, then take a cab to to Colosseum and walk around the outside of it - very impressive. Also Trajan's Column and the Forum are fairly visible without going inside
If they picked the Colosseum, they could go to St. Peters Square and see the church exterior.
Maybe they will feel ambitious and try to go inside one of these, if the lines are ok and they aren't exhausted, but it's not a definite part of the plan.

If they could find some time to go inside the Pantheon, that would be my next suggestion.

Personally I would go the Colosseum route and skip the Vatican (the museum is too crowded for me to appreciate).

Assuming the long flight is from America, and they land in the morning, it would be 1.5 days. If so, they might consider doing the jet lag walk to Trevi, Spanish Steps, Pantheon, Narvona etc since you want to keep moving and they don't require alot of concentration. Then maybe do Vatican or Colosseum early on the second day and anything else they want to hit.

Thank you all for your suggestions!

Maybe you could persuade your friends to visit here themselves. To ask their questions with as much information about personal wishes as possible. Even the most dedicated middleman cannot help but filter something out.

Adding on to this question, can someone please help me out with the timeline for picking up tickets (exchanging vouchers for tickets) and going through security for the Colloseum as well as for the Uffizi in Florence? I'm trying to determine how much time to allow/ how early to get to each place. Like, if I buy tickets online, my understanding is that they aren't actual tickets, but rather, vouchers that I exchange for tickets when I get there. So, if I need to exchange vouchers for tickets, do I need to go through security before or after exchanging them? Is my entry time before or after I go through security, i.e., does it start when I enter the security line or when I'm through it? I'm wondering how much time to allow for going through security, and don't want to miss my entry time because I was waiting in line to pass through security. Thank you!

Also, thanks, Kathy, for the tip about Area Sacra at Largo Argentina!

One more thing, sorry! I've found that kids under 18 are free in Florence (Uffizi, Accademia) but it looks like you have to be an EU citizen AND under 18 to be free in Rome (Colloseum, Forum, Palatine Hill, etc.), is that correct?

it looks like you have to be an EU citizen AND under 18 to be free in
Rome (Colloseum, Forum, Palatine Hill, etc.), is that correct?

No, children under 18 of any citizenship are free at all Italian State Museums. Different rules apply to civic and private museums, like the Vatican. From the (official) coopculture ticketing site:

https://www.coopculture.it/en/colosseo-e-shop.cfm

"FREE, european and non-european people under 18"

I agree with much of the above advice. Here's my 5 cents. Get a streetwise map of Rome. Start at Sopra Di Minerva - Pantheon - gelato at San Crispino, just one small piazza north of Pantheon - San Luigi Church - Piazza Navona and Santa Agnese. If you have time left in afternoon (around 2 pm or so) - go to St. Peter's Basilica. Download a RS free guide to explain the sites. Or, use a RS guidebook or other when walking around Sopra Di Minerva, Pantheon, and St. Peter's.
This way, you won't be jammed up in lines much except for the security at St. Peter's Basilica.

Alternatively, go to the Basilica first. Then, do the walk and end with a lovely meal at Cul-du-Sac located just outside Piazza Navona (SW corner) on Piazza Pasquino. See the small, historic Pasquino statue.
See the cats at Largo Argentina. (It is believed Julius Caesar was killed here.)
There is a famous small (tiny) drinking water fountain near Sopra Di Minerva.
Relax and have fun.

I booked my Rome day trip from https://www.romecitytour.it/, and you could choose to go on the Morning or Afternoon trip.

It was quite handy for me as I was able to arrange other activities on that day and not too rush.

I would definitely recommend visiting the Colosseum and Roman Forum with skip the line tickets as your friends don't want to wait in lines too much.

Thank you all, again, for the wonderful ideas.