How could I indicate in the visa application that I want the visa to be valid for 1 year and with a 90-day duration of stay? I don't know how to show that. Do I do it by the dates of the first and last entries?
When you apply for a Schengen visa, you have to explain the premise of your trip. That means you explain where you want to go, when you want to go, what you are doing there, who pays for the trip, and why the visa officials should believe that you will return to your home country. Your should have a planned date of travel for that.
Typically on the first couple of visa applications you get a single-entry visa with perhaps a few days more validity than your planned trip. Once you have a travel history in Schengen, without overstays or other incidents, and if you appear reliable, you might get a multi-entry visa with a longer validity (but still limited to 90/180).
If you cannot say when in the next year you plan to make the trip, the application seems rather weak for a first-time visitor.
I recently applied for a Greece Schengen visa and was granted a 1 year type C multiple entry visa to the Schengen area. Below are some suggestions that worked for me.
1) This was my third Schengen visa. 2) I was a permanent resident of Canada at the time of application. Before, when I applied for my second Schengen visa in New York, the Finnish consulate was hesitant in issuing a long term visa as I was on a temporary work permit that was expiring the same year. They did issue me the visa, but it was for the exact dates of the trip I'd shown. 3) I had travel insurance for 1 year, it is actually cheaper if you get it 2 times or more within a year. 4) I politely requested the visa officer for a 1 year visa and showed her copies of my previous Schengen visas. She made a note of it, and said she'll take that into account.
PS: My Parents in India also got the same 1 year visa, the second time they applied, so it really depends on the consulate, but hopefully these pointers might help someone.