Dear sir,
Any assesse who only deals in supply of goods can opt for this scheme that means this provision is not applicable for service providers.
There should not be any interstate supply of goods that means businesses having only intra state supply of goods are eligible.
Switching from normal scheme to composition scheme, taxpayer shall be liable to pay an amount equal to the credit of input tax in respect of inputs held in stock on the day immediately preceding the date of such switch over. The balance of input tax credit after payment of such amount, if any lying in the credit ledger shall lapse.
You can opt for composition scheme only at the beginning of the Year.