Start early from Islamabad ... You will have option of 2 routes, via Abbottabad/Mansehra or via Bhurban/Kohala/Muzaffarabad to reach Naran. I personally prefer and suggest Muzaffarabad route as Abbottabad/Mansehra road is mostly very busy and most of the time due to traffic jam, you have to move at snail pace.
Make sure to get fuel tank filled from Balakot as after this point there is no decent petrol pump and you will only find Khula petrol sold from the drums.
You can have brunch/lunch at Kiwai or any restaurant along the river, there are plenty of good restaurants having charpais in the river. Try not to get fooled with fake/farm trout fish.
I suggest to have 1 night stay at Batakundi, its almost 30 min drive from Naran. Don't stay at Naran, it is very crowded and condition these days is similar to Mall road Murree.
Next morning you should leave early for Hunza. On your way you can take small breaks at Lulusar Lake and then at Babusar Top.
From Babusar Top road is very steep, need to drive in low gears and with minimal use of break. You will be going downhill from an altitude of 13700 to almost 4000.
Have Lunch at Besar, one of the best place in this journey.
Road is very good till Chilas, once you reach KKH, road from Chilas to Rai Kot almost 40km is not in good shape. There are few very bad patches, but rest of it is just OK. Drive with patience for the love of your car. Once you cross Rai Kot bridge, road will surprisingly turn to a road to heaven. Almost like motorway.
You should get your tank filled from Jaglot. Jaglot is also junction of 3 of the world's highest mountain ranges, Himaliya, Karakoram and Hindu Kush. You will also find Nanga Parbat view point on your way.
Almost 40 km from Jaglot you have to take a right turn towards Hunza. You should take a break at Raka Poshi view point. One of the best view of Raka Poshi.
You can easily reach to Karimabad before evening. You can stay at Serena or Eagle's Nest best hotels in town, Try to have dinner at Eagle's Nest, the view from there is just wao...
You can also visit Altit Baltit forts in Karimabad.
Next day leave early, have a stop at Atabad Lake, do some boating in the lake, its one of the best experience in this journey. Drive all the way to Khunjerab having stops at Gulmit , Passu etc. On your way you will find farms of apricots and cherries, always a treat to pick some fruit directly from the trees.
You can come back same day from Khunjerab to Karimabad. There are many valleys you can visit, some are accessible with car, some have jeep tracks only.
You can get complete details from this thread https://www.pakwheels.com/forums/t/topic/248873/752
probably one of the best threads on Pakwheels.
(posting without author's permission, hope he will forgive me)