Hi, it depends on your schedule that what season would you preffer to reach out the places and the budget as well. You can start exploring from himachal/uttrakhand.
North India has a diverse landscape. From deserts to mountains, you can find everything here. You can start with exploring the Golden Triangle, i.e., Delhi, Agra and Jaipur. While Delhi is the capital of India where you can find monuments associated with the history of India, Agra is home to Taj Mahal and Jaipur has plenty of forts and palaces that reflect the royal past of Rajasthani kings and queens. You can acquaint yourself with the farms of India at Haryana and Punjab. These states have villages and towns that you can explore alongside the extensive farms. In Amritsar (Punjab), you can also visit Golden Temple. You can also explore the snow-clad mountains of India. Himachal Pradesh and Uttarakhand are easy to reach from Delhi via road. You can also enjoy adventurous activities here such as paragliding (Bir - Billing), river rafting ( Rishikesh), Camping (Kasol) and trekking to various Himalayan peaks. You can also explore the seven sisters of North-east which include Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland and Tripura. Exploring the entire North India would require a lot of time and budget. So, it's suggested to either make a plan as per that, or visit limited places at a time.