Hi,

You can go through the below code

<apex:page standardController="CustomObj__c" extensions="FileUploadController" 
	tabStyle="CustomObj__c" showHeader="true">
	
	<apex:pageBlockSection title="Select a file to be uploaded" collapsible="false"/>

	<apex:outputPanel id="panel_Upload">
		<apex:form id="form_Upload">
			<apex:inputFile id="file_File" value="{!fileBody}" filename="{!fileName}"/>
    			<br/>
			<apex:commandButton id="button_Upload" value="Upload" action="{!processUpload}" />
		</apex:form>
	</apex:outputPanel>
	<br/>
</apex:page>


public class FileUploadController 
{
	private String fileName;
	private Integer fileSize;
	private Blob fileBody;

	public FileUploadController(ApexPages.StandardController controller){}

	public FileUploadController(){}


	public String getFileName()
	{
		return this.fileName;
	}
	
	public void setFileName(String fileName)
	{
		this.fileName = fileName;
	}
	
	public Blob getFileBody()
	{
		return this.fileBody;
	}
	
	public void setFileBody(Blob fileBody)
	{
		this.fileBody = fileBody;
		setFileSize(this.fileBody.size());
	}

	public Integer getFileSize()
	{
		return this.fileSize;
	}

	public void setFileSize(Integer fileSize)
	{
		this.fileSize = fileSize;
	}
	

	private Database.SaveResult insertCustomObject()
	{
		CustomObj__c custObj = new CustomObj__c();

		// fill out cust obj fields

		return Database.insert(custObj);
	}

	private Database.SaveResult insertAttachment(Id parentId)
	{
		Database.SaveResult result;
				
		Attachment attachment = new Attachment();
		attachment.Body = this.fileBody;
		attachment.Name = this.fileName;
		attachment.ParentId = parentId;
		
		result = Database.insert(attachment);

		fileBody = Blob.valueOf('  ');
		return result;
	}

public PageReference processUpload()
	{
		try
		{
			Database.SaveResult result = insertCustomObj();
			
			if (result == null || !result.isSuccess())
			{
				return null;
			}
	
				
			result = insertAttachment(result.getId());

			if (result == null || !result.isSuccess())
			{
				return null;
			}

		}
		catch (Exception e)
		{
	            ApexPages.AddMessages(e);
		}

		return returnUrl();
	}
}

Thanks,

Devendra