As Gaurav put it " You can never come back from the mountains ", not a single week goes by where we do not recollect memories from the trip, and hope to get back asap. The scale of the himalayas is not something words or pictures can justify, you have to be there to really feel it. The terrain, and the people change drastically from himachal, to ladakh, to Kashmir.
1. Ride with a group like rideofmylife. They provide backup rider/vehicle, road captain, mechanic, carry luggage, arrange accommodation.. basically you just go report on time..
or with friends as the roads are very isolated, and far from civilisation(but solo trip would be epic :) ).
2. Long water proof boots are a must to wade through ice cold water. Carry lot of spare socks too
3. Riding gear, and water proof gears are a must.
4. Carry lots of energy bars/chocolates/biscuits. Food options are very few, and eat up when you find one on the road.
5. Carry thermals/warmers for the night, as temp drop in the nights.
6. Smile - the locals are very friendly.
7. Union checkpost create issues if the bikes/car are not in your own name(owner has to be with you). Rented bikes from other states will only be allowed till Leh, then they insist on you renting locally(they wont allow you to go to pangong or hunder..). You can ride across to srinagar, but not for local sight seeings
8. Get used to altitude by reaching manali a day or 2 earlier, and use high altitude acclimatisation medicines recommended from a Doctor if needed(recommended). If Altitude sickness hits you, do not take risks, plan to consult a doc, and end your journey if advised.