In addition to Carteblanc's point

I'd also recommend playing custom games like monobattles or just games with friends off ladder.  The biggest danger when you restart is doing too much and burning yourself out.  Concentrate on simple things at first and add more in as you get used to the sheer weight of playing games. 

Also remember, it's dangerous to go alone!  Get friends either from here or other people you know to play with you.  It makes everything more manageable.