Hi you can try this,

<apex:page controller="FileUploadController" showHeader="false">
<apex:sectionHeader subtitle="Attach Documents"/>

<apex:form enctype="multipart/form-data">
<apex:pageMessages />
<apex:pageBlock title="Upload a File">

<apex:pageBlockButtons location="Bottom">
<apex:commandButton action="{!upload}" value="Save"/>
</apex:pageBlockButtons>

<apex:pageBlockSection showHeader="false" columns="1" id="block1">

<apex:pageBlockSectionItem >
<apex:outputLabel value="File Name" for="fileName"/>
<apex:inputText value="{!document.name}" id="fileName"/>
</apex:pageBlockSectionItem>

<apex:pageBlockSectionItem >
<apex:outputLabel value="File" for="file"/>
<apex:inputFile value="{!document.body}" filename="{!document.name}" id="file"/>
</apex:pageBlockSectionItem>

<apex:pageBlockSectionItem >
<apex:outputLabel value="Description" for="description"/>
<apex:inputTextarea value="{!document.description}" id="description"/>
</apex:pageBlockSectionItem>

<apex:pageBlockSectionItem >
<apex:outputLabel value="Keywords" for="keywords"/>
<apex:inputText value="{!document.keywords}" id="keywords"/>
</apex:pageBlockSectionItem>

</apex:pageBlockSection>

</apex:pageBlock>
</apex:form>
</apex:page>

public with sharing class FileUploadController {

public Document document {
get {
if (document == null)
document = new Document();
return document;
}
set;
}

public PageReference upload() {

document.AuthorId = UserInfo.getUserId();
document.FolderId = UserInfo.getUserId(); // put it in running user's folder

try {
insert document;
} catch (DMLException e) {
ApexPages.addMessage(new ApexPages.message(ApexPages.severity.ERROR,'Error uploading file'));
return null;
} finally {
document.body = null; // clears the viewstate
document = new Document();
}

ApexPages.addMessage(new ApexPages.message(ApexPages.severity.INFO,'File uploaded successfully'));
return null;
}

}