One day in Rome

Hi
See what your time is for the Borghese is first, there is an electric bus that goes into the park and stops very close. This will take you via the Colosseum into or from the centre of Rome. A combined bus/metro day ticket would be just the thing and you can get bus advise over at "Ron in Rome". Rome buses has a website so you can download a route and bus number map before you go . There is also a metro stop just in front of the Colosseum.
A combination of bus, walking and metro will get the most out of that day, you might also have time for the Sistine Chapel.
regards

I always like to start at the site that I want to see the most of. I would start at the colosseum and work back. You may also want to consider booking a private guide for the day or 5-8 hours. We contacted Through Eternity Tours for our roman holiday and told them what we wanted to see. They arranged a guide and created a custom tour. It was costly but an amazing use of our time. We got so much more out of our visit. When you are short on time, and want to get the most out of your visit, it might be something to consider.

You need to reserve your ticket for the Borghese Gallery - first time is 9 am and last is 5.00 pm and you are in the gallery for 45 minutes. Book it online before you go.

At the Colosseum you will encounter lineups but you can buy tickets online before you go. Opens at 8.30 closed at different times depending on when in the year you go.

Both are well worth visiting - as is the Pantheon. But do take some time for the great Roman past-time of sitting, having a drink and watching the world go by!

Don't waste your time putting the Spanish Steps on your agenda. It was on my "must see" list my first time to Rome, and it's so inconsequential, that I walked by it (them) without even noticing.

I've been to Rome at least 6 times now, and seen most of it, and I would advise getting in the taxi, and seeing the Colosseum, even just a drive-by. I'd make sure to go to the Trevi, get a gelato and toss your coins in, because one day in Rome is simply not nearly enough. One thing I'd make sure of, is seeing the Sistine Chapel. Really and truly one of Rome's wonders!

The other poster who suggested the private guide was probably giving the very best advice. I'd also add Campo di Fiore in the morning, or don't go, and Piazza Navona. You can have a meal (lunch) at Piazza Navona and in the beauty of Rome. The fountain and square are magnificent. The Pantheon is within walking distance of there, and you can "pop in" for a minute, Beautiful!

Thank you so much to everyone for your comments! We pondered the guided tour option but decided to go our own route so we could add time or spend as little as needed at each stop. Here's a recap of our day in Rome (assisted by printed walking directions from Google Maps):

1) Taxi to Colosseum, opted to walk around the outside instead of going in. Amazing and the moment it was "real" that I was in Italy. Not going to lie, I got misty eyed. My trip of a lifetime was really happening! We opted not to go in as a good portion was under scaffolding and wanted to see as many other things as we could. Still amazing just walking around the outside and peeking in.
2) Arch of Constantine. Right next to the Colusseum, half under scaffolding but you can still get pretty close to see the details.
3) Roman Forum & Palentine Hill - spent quite a bit walking around in here. Same ticket gets you into the Colosseum.
4) Piazza Venezia / Altar of the Fatherland (Passed by on our way to Compidoglio simply because we went the wrong way to #5, still impressive from the outside)
5) Compidoglio Square (will go back here for the museums surrounding it next time!) Designed by Michaelangelo.
6) Piazza Narvona. Two fountains with an obelisk in the middle. Wonderful to see the people walking around, look at the fountains, see the little market that was set up in the square. I enjoyed looking at the buildings surrounding the piazza just as much as I did walking around in the square.
7) Pantheon - surprised to find out it was an active church. The engineering boggles the mind when you consider how long ago it was completed.
8) St. Maria Sopra Minerva Basilica. The second of many, many churches we went into. So plain from the outside, we didn't even think it was open. Inside, absolutely amazing frescos, interesting that they have little boxes and for .50 you can illuminate them for a short time for a better look. One of the top five of all the churches we visited. (note if there is someone outside collecting money "for the brotherhood" they are not associated with the church)
9) Church of St. Ignatius of Loyola. Again, very plain from the outside (not as plain as above) but the ceiling took my breath away. These two churches were within a 5 minute walk of the Pantheon yet hardly anyone was in them. These two set a very high bar and (unfairly) were what we compared a lot of other churches to.
10) Trevi Fountain - yes, I threw a coin in.
11) Spanish Steps - Mom wanted to see the steps and since it was on our way back to the hotel we stopped by. I agree with the above comment as we also walked passed it the first time (the boat shaped fountain {?} at the bottom was under scaffolding). We went up the steps and off to the hotel.

Overall it was an amazing day - we walked from 11am until 6:30pm, enjoyed a slice of pizza and gelato (the first of many) along the way. Thank you again to those that commented above, you helped make the start of our tour one we will never forget!