Dear Durgaji;
Love.
Your question is vague hence appropriate answer will not be possible. However I give you few tips, which may help you.
1) Fulfill legal formalities.
2) If you don't have budget constraints, then take services of a professional to design your mobile van and also to market your products.
3) Decide the product mix and tariff considering the taste and economic condition of the locals.
4) Remember that location, timings, cleanliness, hygiene and freshness of the food are very important factors to be taken care off.
If you write further details, better guidance can be given. Anyway I wish you all the best for your new venture.
His Blessings;
Sharad Shah