1. Make sure the reflectors are in good nick and the glasses aren't steamed up, if they're knackered get new headlamp units.
2. Rewiring the headlamp and main beam circuits with two 30A relays direct from the battery ensures there is minimal resistance in the headlamp circuit and takes the load off the notoriously weak stock healamp switch and wiring
3. Once you've rewired, the circuit is then up to taking high wattage bulbs. I have 90/100W in mine. Headlamps are now great. (and yes I know they're illegal but if they're adjusted properly they don't dazzle anyone so who cares)