Since nobody else is responding, I'll take a crack:

In your shoes, I'd take the L train into Manhattan and get off at Union Square.

At Union Square I'd do the free transfer to the #4 train heading to Brooklyn.

At Franklin Avenue I'd transfer to the #3 train and get off at Nostrand Avenue (which should be right at Eastern Parkway).

There are shorter routes (such as connecting between routes in Brooklyn), but they would involve more changing of trains.