Follow these:

VF PAGE: On your VF page where you have added Account lookup, add actionSupport. On change of Account lookup value this will call another method in your controller which will query the Account record slected and populate other fields that you want. Also this will rerender other fields on the page with the new values you have just queried

<apex:inputField value="{!tObj.Account__c}">
        <apex:actionSupport event="onchange" rerender="panel1" action="{!populateOtherFields}"/> 
 </apex:inputField>

<apex:outputPanel layout="block" id="panel1">
	<apex:inputText value="{!accIndustry}"/>
	<apex:inputText value="{!accNumber}"/>
</apex:outputPanel>

 APEX CLASS:

public String accIndustry {get;set;}
public String accNumber {get;set;}
public PageReference populateOtherFields()
{
	Account a = [Select Id, Industry, AccountNumber from Account where Id=: tObj.Account__c];
	accIndustry = a.accIndustry;
	accNumber = a.AccountNumber;
	return null;
}

I have typped the above code for your reference, it might have some typos etc. Use this for your refernce and add error handling etc.

IMP: If you have some required fields on the page, you might face some issues while rerendering and have to use actionregion tag here. To validate this functionlity, which you select an Account, fill all the required fields on the page firsy, if you have any,