By road
Rawalpindi has extensive road networks, linking it directly to various major cities such as Lahore, Peshawar and Taxila to the north.Apart from that the twin city, which Rawalpindi is otherwise called, has a complete structure of traveling around in the city through local buses. However, this is not a recommended mode of transport to tourists. Taxis are cheap, and you'll be looking at around Rs250 or so for a trip from Ghakar Plaza to the outer sectors of Islamabad, so travel within Rawalpindi will be around Rs100 per trip - very affordable for a foreign tourist. Make sure you agree the price before getting into the taxi.
By train
Rawalpindi has its own central railway station, with regular sevices to many destinations within Pakistan.
By bus
Skyways and Daewoo are 2 of the nicer long-haul operators. Skyways offer some direct services to/from Islamabad and Lahore, Peshawar and Karachi. Daewoo has its own terminal on the road from Islamabad just outside Rawalpindi. You can call the Daewoo Station in advance for booking. They shall confirm a seat for you. The number is 051 111 007 008. You can travel to Peshawar, Lahore, D I Khan, Murree, Sialkot, Abottabad, Bahawalpur, Faisalabad, Multan, and recently they have started service between Karachi and Hyderabad [cited from Islamabad page]
Coach is a very comfortable way to travel in Pakistan, and is very popular for travellers between Rawalpindi and Lahore. You will receive a small meal on the coach, and a first class ticket is between Rs1000-Rs3000.