With so many fantastic native plants on the market I’m sure most people would have at least one Grevillea, Banksia or Callistemon in their garden.
Grevillea with LorikeetOver time they can become scraggly and require trimming. The best time to do this is in the warmer months, but should yours need extreme pruning for what ever reason, then during summer is the time to attack it.  Remember to give it a good watering afterwards and some native food & decomposing mulch for ongoing support.
If time allows consider the flower cycle and the birds dependent on the nectar, but otherwise I have seen Grevilleas taken back really hard, basically to stumps and they come back even better!  
  Gardening Gift Voucher