What is a good guide that shows new Android users how to properly backup and Flash a new ROM? I've had my Samsung Captivate for almost a year now, It's my first smartphone, and I've just recently decided to root it. Being new to root and not having the greatest understanding of the Android system or the Linux/Unix system I still want to install CyanogenMod.

Does anyone know a good guide for someone like me? It doesn't have to be CyanogenMod specific.
CyanogenMod has a good overview with many devices and a full update guide per device (Captivate as example here). Here is an explanation of commonly used terminology (fastboot, adb…).

There are some differences between manufacturers/brands:  


Google: very easy, with standard tools (adb, fastboot)
Sony: rather easy, all standard tools + special tool (flashtool by androxyde), locked bootloader that needs an unlock code from website (not possible for all branded phones)
Motorola: rather hard to mod, locked bootloaders
Samsung: rather easy, unlocked bootloaders (except for some branded phones)