Hey Yasmin, Himachal is a big state you will need ateast a month to cover all the state. Depending on my experiences you may follow this route: Chandigarh ->Trithan Valley (5 Days ) ->Mandi-Prashar Lake trek (2 Days) ->Parvati Valley-Malana,Kasol,Tosh,Kheerganga trek (5Days) ->Kullu-Manali(3 Days). You can go to Dharmshala-( Macleodganj,Triund trek,Dalhousie,Khajjiar). And for the activities 1)Rafting at Kullu 2)Skeeing at Manali 3)Paragliding at Bir (Dharamshala) or Kullu Hope this would help in your plan.
You can make a round trip Starts from Shimla- Nako- Kaza- Spiti-Rohtang Pass- Manali-kullu -tirthan valley. But this will require minimum 10 to 12 days. Don't go in winter Because Roahtang Pass will be closed in winters due to heavy snowfall.
Hi Yasmin, the best way to cover Himachal pradesh is in HRTC buses, they have connectivity to even the remotest places. I'm also attaching with this message a post about map of hostels in Himachal, you can go through it and plan your trip.