Instructions
Get a pricing guide that lists your train, such as Greenberg's. It publishes guides for several brands of antique trains, such as Lionel, Marx and Ives. Some guides are available at your public library. You may need to visit a model train dealer for some others.
Check the prices for identical trains in the same condition on eBay, and see what prices they have sold for. Also check out train swap meets and see if there are similar sets available. At swap meets you can talk to experts and dealers from around the country about what you have. They may be able to point you right to a buyer willing to pay top dollar.
Post your trains on eBay after you determine their worth. It may be worth your while to pay to get your trains fixed or restored, provided original paint and parts are used. But be careful how this is done; improper restoration can drastically reduce the value of the train.
Or, negotiate directly with buyers or dealers at swap meets. You may encounter someone who desperately wants your train and is willing to pay more than its market value to get it quickly and easily.
Or, sell your train to an institution that would display it. This allows you to reap the proceeds of the sale and then perhaps be able to view it on display from time to time. If you cannot find a buyer for your train, consider donating it to an appropriate institution for a tax deduction equal to its fair market value.