I've gone before and will be moderating a panel on projection mapping this year.  There's a TON of SXSW newbie web sites, would recommend just googling "SXSW newbie". 

It is a pretty overwhelming experience.  It's awesome and really fascinating, but is huge, so really pays to preplan a bit.  Study the session guide and strategize locations…the sessions take place in multiple buildings/locations.  Also helps to have backup choices if a session doesn't end up being that interesting…  And most of all TAKE BREAKS…  You can really run yourself ragged, so don't worry about missing something.

Also, check out the variety of lists of parties (there are a ton!  Never pay for any food or drink) that will start popping up in January… You will want to start RSVPing to them