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.
Contacts. If you are a high profile individual/business contact the consul-General of the consulate you will be applying from. I was told that the maximum length of you first visa would be 6 months but they could issue a 2 year visa the next time you applied.