Microsoft had released a set best practices for many common types of customizations Microsoft SharePoint Products and Technologies.

Check it out SharePoint Products and Technologies Customization Best Practices  - Interesting one!!!… 

·         SharePoint Database Schema Change

·         SharePoint Database Access

·         Modifying Built-In SharePoint Files

·         Web Services Access

·         SharePoint Designer Editing

·         SharePoint Solution

·         SharePoint Feature

·         Feature Stapling

·         Feature Event Receiver

·         Windows Server Service

·         Timer Job

·         Web Application

·         Web Service

·         Site Definition

·         List Definition

·         Site Template

·         List Template

·         Field Type

·         Content Type

·         Column Template or Site Column

·         Delegate Control

·         Form Template

·         Custom Action

·         _Layouts Page

·         Event Handler

·         Backward-Compatible Event Handler

·         Coded Workflow

·         No Code Workflow

·         Workflow Activity

·         Workflow Condition

·         Web Part

·         SharePoint Theme

·         Document Icon

·         IFilter

·         Document Converter

·         Information Management Policy

·         Business Data Catalog Application Definition File

·         Excel Services User-Defined Function

·         InfoPath Form Custom Code

·         InfoPath Form View Control

·         HTTP Handler

·         HTTP Module

·         Pluggable Authentication Provider

·         Pluggable Single Sign-On Provider

·         STSADM Command Extension

·         Inline Code

·         web.config file Settings Change

·         Security Policy