Will be going to The Galapagos, Cuzco/Sacred Valley etc, Lake Titicaca La Paz, Cochabamba (probably), the Salt Flats than making our way down to Santiago. Over the period of 6 weeks.
Any tips from those who have been there, done that would be greatly appreciated. :-)
Have a great trip. Those are amazing places to visit.
Some tips:
Learn as much Spanish as you can before you go. You'll be able to get around fine without it but you'll just have a much richer experience if you can interact with the locals.
Eat at local restaurants - the "Menu del dia" (menu of the day) is an easy option and will give you a local experience.
If you are travelling by bus between towns try to get the best one you can. This will usually come with big comfy seats, meals and drinks, and wifi. Although the local buses can be an interesting experience.
Take as much time to acclimatise as you can when you get to altitude. The first few days at least will be a struggle. This will probably be in Cusco which is very comfortable. There is lots to see in the Sacred Valley. Moray is an interesting sight that many tourists miss.
Lake Titicaca is much better from the Bolivian side. You'll probably do the boat trip to the floating islands from Puno. It is an underwhelming and touristy experience, don't worry though because everyone does it. Take a day trip to the Isla de Sol (Island of the Sun, from Copacabana).
Colca Canyon is worth a visit if you have the time but might be too much out of your way.
The Salt flats are amazing. We did the trip from Tupiza to Uyuni via 4wd. This is probably the opposite way you are going. I really recommend the longer tour, probably Uyuni to Tupiza over 3? days, rather than just out and back again from Uyuni.