ITR Filing - Please help me

you have all the details of sales right enter those in tally or excel.

Also find out what other details you can gather from him especially use his bank pass book and also check the sales with VAT Statements.

You can also enquire from him  about the cash sales if any.

generate sufficient cash and clear the expenses on the basis of details given by the assessee.

since he has not maintained books accounts income tax can be as per 44ad presumptive basis.for this you should have info regarding the sales made during the year ,bank /cash balance at year end net profit

related to nature of turnover he must have been registered under state Vat/ CST or service tax, 

pull out the summery from those returns and make gross turnover as per related acts, 

for gross receipts use bank statement, 

for expenses also use bank statement

for closing balance of stock , cash, debtors, creditors, get the owerns statement.

ask him to submit as much details as he can, viz electric bills, telephone, travelling, rent , licence, taxes paid etc. 

ask him for fixed assets, and claim depriciation on them.

Why don't u go for Section 44AD, presumptive taxation.