Make sure you have all the parts / tools you need before you start.
You will need to buy a new head kit which includes new stretch bolts, head casket, rocker cover seals, timing belt.
If you have no or limited history with the car then please consider buying the full belt kit which includes the tentioner pully (prone to fail, so worth changing)
its also a good time to replace the water pump
Its recommended to have the head skimmed and pressure tested.
But it all depends on budget and the extent you want to undertake preventative maintenance.
Its also worth investing a few quid in a timing jig which is used to help line up the twin cam sprockets (about £6)