Preparation before you install Exchange 2013 in existing organisation

1. There are only two roles now for Exchange 2013, CAS and MBX. You can only install Exchange 2013 with CU1 or later.
2. If you will use the legacy method, configure second internet ip to point to an A record called legacy. In the FW point both ip addresses to the old exchange server. 
3. Upgrade all the existence exchange servers to the latest sp3 and rollup. You can’t upgrade from exchange 2003.
4. Supported Clients:

• Outlook 2013 (15.0.4420.1017)
• Outlook 2010 Service Pack 1 with the Outlook 2010 November 2012 update (14.0.6126.5000). For more information, see Description of the Outlook 2010 update: November 13, 2012. 
• Outlook 2007 Service Pack 3 with the Outlook 2007 November 2012 update (12.0.6665.5000). For more information, see Description of the Outlook 2007 update: November 13, 2012. 
• Entourage 2008 for Mac, Web Services Edition
• Outlook for Mac 2011

5- Hardware needs to be 64bit processors, Xeon is the preferred with 8GB memory will be a good start.
6- The supported OS is either 2008 R2 sp1 or 2012
7- In a multi-server scenario these are the requirements:
• Schemma is windows 2003 sp2
• Domain Function level can be 2003
• Forest level is 2003
• DNS is a Multi-label DNS online.local
8- Additional Components:
• .NET Framework 4.5
• Internet Information Services (IIS)
• Windows PowerShell V3.0 you can use Get-Host to determine the version
• Windows Management Framework V3.0
9- Two versions of CAL for Exchange, Standard and Enterprise.. The Enterprise CAL allows for the use of unified messaging, advanced compliance capabilities and antivirus / anti-spam facilities.
10- To use the advance features in Exchange 2013 like UM voice message to email and auto-archiving you need the Client Standard license plus the Enterprise one.
11- Sales bought SSL certificate with a multi-domains capability.
12- Ensure the RPC-Over-HTTP service installed as well.
13- Change WinRM services to automatic and type the following command in PowerShell:
Enable-PSRemoting -Force
14- To do the prerequisites
For the Windows 2012

• Install-WindowsFeature AS-HTTP-Activation, Desktop-Experience, NET-Framework-45-Features, RPC-over-HTTP-proxy, RSAT-Clustering, RSAT-Clustering-CmdInterface, RSAT-Clustering-Mgmt, RSAT-Clustering-PowerShell, Web-Mgmt-Console, WAS-Process-Model, Web-Asp-Net45, Web-Basic-Auth, Web-Client-Auth, Web-Digest-Auth, Web-Dir-Browsing, Web-Dyn-Compression, Web-Http-Errors, Web-Http-Logging, Web-Http-Redirect, Web-Http-Tracing, Web-ISAPI-Ext, Web-ISAPI-Filter, Web-Lgcy-Mgmt-Console, Web-Metabase, Web-Mgmt-Console, Web-Mgmt-Service, Web-Net-Ext45, Web-Request-Monitor, Web-Server, Web-Stat-Compression, Web-Static-Content, Web-Windows-Auth, Web-WMI, Windows-Identity-Foundation
• Install-WindowsFeature RSAT-ADDS

For 2008 R2 use the following:
a- Import-module ServerManager
b- Add-WindowsFeature NET-Framework,RSAT-ADDS,Web-Server,Web-Basic-Auth,Web-Windows-Auth,Web-Metabase,Web-Net-Ext,Web-Lgcy-Mgmt-Console,WAS-Process-Model,RSAT-Web-Server,Web-ISAPI-Ext,Web-Digest-Auth,Web-Dyn-Compression,NET-HTTP-Activation,RPC-Over-HTTP-Proxy –Restart

15- On servers that will host the CAS or Mailbox server role, install the Microsoft Filter Pack. Download and install the following:
• Microsoft Unified Communications Managed API 4.0, Core Runtime 64-bit
• Microsoft Office 2010 Filter Pack 64 bit
• Microsoft Office 2010 Filter Pack SP1 64 bit

16- Make sure the server is up to date in securities
17- Setup will do these commands but in multi-server installation it will be preferred to run them manually so you can assess the reaction of each one. Run these commands to upgrade the Schema setup.com /PrepareSchema, Domain setup.com /PrepareAD,