You need to adjust your rear brake shoe clearance so they are as close as possible to the drums without rubbing, then you need to take as much slack out of the cable run as possible, but you also ideally need to adjust the transfer arms so that the bell crank is applying maximum leverage to the shoes when the handbrake is in the engaged position.
On my 1986 car the transverse rods are pretty much non-adjustable but I found I could get the necessary efficiency to pass an MOT by taking all the slack out of the main cable. It's still not brilliant on really steep hill starts though, sometimes I have to resort to heaving on the handle to provide a bit of extra braking force while I go from brake pedal to throttle to pull away.
