First time flashing and customizing my k800i

Hello there, i am new to this whole customizing and flashing thing, i have a k800i CID52 which i would like to customize, i havent done anything to it yet, i just wanted to know the first thing i should do to it before everything else, apart from maybe backing up my GDFS and would also like to know, which software should i use, SE Tool or XS+ I have both, i am mainly interested in installing elfs and ofcos some other features, any assistance will be greatly apprecited