1. The road till Reckong Peo is perfect and you'll not take much of time stuck with bad roads there. The traffic will delay your journey in case you're travelling from the Simla route.
2. Don't drive after 6 until and unless it's necessary.
3. Keep warm clothes for yourself and get some moisturizer and sunscreen lotion as you'll get good amount of uv rays in Spiti.
4. You'll get good home stays in any village you'll cross in that route. Try staying there and listen to the stories from the people. It's an experience in itself
5. Keep yourself hydrated and enjoy the beauty of valley. Don't drive to fast unless it's required. Roads are narrow and stone pelting happens.
6. Don't miss out on places in Spiti. Each village has it's own charm, beauty and history. Spend time there and interact with local people.
7. Temperature at night is usually below 0 degrees. Be prepared for that.
8. There's less oxygen so don't run and trek if you're not a regular trekker in Himalayan range.
9. Enjoy local cuisines and visit monasteries to know more about the place and culture.
10. Places to visit: Kaza, Nako, Kibber, Langza, Chicham, Mudh, Dhankar, Tabo, Gluee
11. On your way back, visit Chitkul if you've time. Chitkul is on the China border and has got beautiful climate and snow glaciers around.
12. There's no petrol pump between Reckong Peo and Kaza. Get it full from there and keep extra petrol or diesel in car. Even if you fell short of it, don't panic, you'll get it at an extra cost from a local shop.
Let me know if you need anything specific to know.
Wish you a great journey ✌🏻