You should take a bus near to the subway station "Ulitza Dybenko" in St .Petersburg to the Kirovsk town (25-30 min - 1.5 euro). Then from the central square of Kirovsk your way lies down the Neva river by the road to St.Petersburg (3 km - by the foot 30-45 min). Road goes on a river side, pass by famous "8th GRES" (8th electric power-station). When you see the war memorial - anti-tank gun ZIS-3 on right side of the road, it will mean that you are on the north border of the bridge-head.
There is also bur route from Rybatzkoe sub-way station in St.Petersburg to Kirovsk-Schlisselburg. You can get just to the bridge-head within 40-50 min.