Highland driving (F-roads) is very different from other driving. Conditions change quickly, there are unbridged rivers to cross, the „roads“ are rough and driving slowly is important.
Notice that not all 4WD vehicles are good for the F-roads! Some F-roads are OK for a Dacia Duster (or similar), for others you need a Toyota Landcruiser (or similar/bigger) and then for some you need a modified vehicle (superjeep).
Do notice that no insurance covers the damage of a vehicle while crossing a river!
First thing to check: if the F-roads in the area are open by now. See here: https://umferdin.is/en
They‘re usually closed mid September until June/July. During that period the roads are closed/impassable for anyone not in a modified vehicle (superjeep) and if you want to get there, you need to book a modified vehicle with an experienced driver.
Get all the information you can on the area you plan to travel around, for example from Safetravel, information centers in the area, rangers and hut wardens.
Off-road driving is strictly forbidden. F-roads and gravel roads are not off-road driving, when you drive off them it is.