I'm just getting my girlfriend into the game, I bought her the Deckbuilder kit, then after I looked through what she got with her, I advised her to make a black-green deck (There was a fair amount of Infect, and some bits of other things, sadly not enough of any theme to build a single solid theme, but all in all it was a good does of a lot of staples, which is why I got it for her). Don't worry about having a solid deck up front, no one expects you to be elite right from the get go... Just build what you can, then trade around and buy other stuff as you go.
So my advice is just get a good start of cards to call your own, be it a fat pack, a few dozen booster packs, a deck builder kit or just a massive wad of assorted randoms... and build your first deck, don't worry about what's easiest to learn, eventually you'll learn most of them, build with what you have, if you have lots of zombies, build a zombie deck, lots of mill build a mill, if you have to stretch out to two or three themes, that okay at first, just try to reign it in as you go, eventually you want it to be just one theme per deck, but you can't always get that right away.
My last piece of advise is a common quote me and my friends used to throw around the table
"First Rule, read your (edit) cards.
Second Rule, read your (edit) cards
Third rule, read your opponents cards."