Dynamic DNS or Domain, free at No-IP VPN — highly recommended, Screen Sharing or VNC can be easily intercepted, you should really use a VPN. VNC client — Mocha VNC or similar, I use Mocha regularly and it is reliable and stable. It supports keyboards too, you probably do not want to use on screen for extended typing.
On your Host , make sure to enable Screen Sharing, connect to your VPN with your iPad, iPhone or other device — most tablets, phones and computers support common VPN protocols, and VNC. Connect to your VPN, and then use the VNC app to connect, you’re good to go!
If you’re using Back to my Mac on an Airport router, you will need to disable the iCloud account in Airport Utility, or you will not be able to connect to the VPN from an outside network. The port forwards will seem to be applied, but when you go to connect it will fail.
Apple must be using the same ports or VPN technology for Back to my Mac. Note that you will need to remove this using the OS X utility, not the iOS version as it is not visible there.
I have not experimented with having both active, as VNC+VPN will run on pretty much any operating system, I wonder if Apple are going to make a Back to my Mac client for iOS though, it may be more elegant than this.