In a recent project, I have to update certain fields of sitecore item when the item is saved in sitecore.

The solution I went for involved extending item:saved event and adding my own handler to do certain actions based upon template type

If you are in a similar situation, here are the steps to do

1. Create you custom class with a public method to perform your logic
2. In web.config under <events> find , <event name=”item:saved”> and append your handler at the end.

Here is basic class code

public class ItemSaveEventHandler
{
//master database name
public static readonly string Master = "master";
//sample template id
public static readonly string TemplateIdItem = "{67B44133-70CD-405C-BDAF-B93E5AEA2682}";

public void OnItemSaved(object sender, EventArgs args)
{

Item temp = Event.ExtractParameter(args, 0) as Item;
//make sure you are in edit mode and not in publish mode
if (temp != null && temp.Database.Name.ToLower() == Master)
{
//check if the template is what you are looking for
if (temp.TemplateID.ToString() == TemplateIdItem )
{
//do your stuff with the item, this is just a sample
temp.Editing.BeginEdit();
temp.Fields["Title"] = "new item saved title";
temp.Editing.EndEdit();
temp.Editing.AcceptChanges();

}

}

}

Complie and debug code, when you are ready change the web.config

<event name="item:saved">
<handler type="Sitecore.Links.ItemEventHandler, Sitecore.Kernel" method="OnItemSaved"/>
<handler type="Sitecore.Globalization.ItemEventHandler, Sitecore.Kernel" method="OnItemSaved"/>
<handler type="Sitecore.Rules.ItemEventHandler, Sitecore.Kernel" method="OnItemSaved"/>
<!-- add the namespace name and assembly dll name as per your site -->
<handler type="<MyWebsite.Handlers.ItemSaveEventHandler>, <MyWebsite.Hanlders>" method="OnItemSaved"/>
</event>

Thats it, if everything is correct the event handler will be called when someone saves an item in sitecore

Cheers