Either of the two ways can work, provided you don't seek peak weeks (e.g., when kids are on vacation). To trade first and then reserve, you'll have to hope that the week you want to reserve is still available. To reserve first and then trade, you'll have to hope that II will match you for the week you want in exchange.
However, the easiest way to do it is as cp73 suggests: buy two of the same EOY - either both even years or both odd years.